Hierarchical communication system using premises, peripheral and vehicular local area networking

ABSTRACT

A hierarchical communication system is described in which wireless local area networks (LANs) exhibiting substantially different characteristics are employed in an overall scheme to link portable or mobile computing devices. In a premises LAN, a series of radio base stations and a backbone LAN make up an infrastructure network. The infrastructure network and at least one mobile computing device make up a higher-power LAN, utilizing a frequency hopping protocol. A lower-power LAN allows for radio communication between a mobile computing device and peripheral devices, utilizing a single-frequency spread spectrum protocol. A vehicular LAN provides for short-range communication between a vehicle terminal and a portable terminal. When out of direct RF range of the premises LAN, the vehicle terminal maintains indirect communication when necessary with the premises LAN via one of several alternate RF channels. A microprocessor, located inside radio units which participate in multiple LAN&#39;s, selects the appropriate protocol, frequency band and power level for communicating through the network.

CROSS REFERENCE TO RELATED APPLICATIONS (Claiming Benefit Under 35U.S.C. Secs. 119-120)

This application is a continuation of U.S. application Ser. No.08/279,148, filed Jul. 22, 1994 and issued Aug. 12, 1997 as U.S. Pat.No. 5,657,317, which is based on PCT Application Ser. No.PCT/US94/05037, filed May 6, 1994, now abandoned, which in turn is basedon U.S. application Ser. No. 08/198,404, filed Feb. 22, 1994, nowabandoned, which is itself a continuation of U.S. application Ser. No.08/198,452, filed Feb. 18, 1994, now abandoned, which is in turn acontinuation-in-part of U.S. application Ser. No. 08/168,478, filed Dec.16, 1993, now abandoned, which is itself a continuation-in-part of U.S.application Ser. No. 08/147,377, filed Nov. 3, 1993, now abandoned,which is in turn a continuation-in-part of U.S. application Ser. No.08/101,254, filed Aug. 3, 1993, now abandoned, which is in turn acontinuation-in-part of U.S. application Ser. No. 08/085,662, filed Jun.29, 1993, now abandoned, which is itself a continuation-in-part of U.S.application Ser. No. 08/076,340, filed Jun. 11, 1993, now abandoned,which is in turn a continuation-in-part of U.S. application Ser. No.08/062,457, filed May 11, 1993, now abandoned.

U.S. application Ser. No. 08/198,452, filed Feb. 18, 1994, nowabandoned, is also based on PCT application Serial No. PCT/US93/12628,filed Dec. 23, 1993, now entered into national phase, which is itselfbased on U.S. application Ser. No. 08/027,140, filed Mar. 5, 1993 andissued Feb. 11, 1997 as U.S. Pat. No. 5,602,854, which is itself acontinuation-in-part of U.S. application Ser. No. 07/997,693, filed Dec.23, 1992, now abandoned, which is itself a continuation-in-part of U.S.application Ser. No. 07/982,292, filed Nov. 27, 1992, now abandoned,which is itself a continuation-in-part of U.S. application Ser. No.07/700,704, filed May 14, 1991, now abandoned, which is itself acontinuation-in-part of U.S. application Ser. No. 07/699,818, filed May13, 1991, now abandoned.

The U.S. application Ser. No. 08/279,148, filed Jul. 22, 1994 and issuedAug. 12, 1997 as U.S. Pat. No. 5,657,317, is also a continuation-in-partof U.S. application Ser. No. 08/205,639, filed Mar. 4, 1994 and issuedSep. 10, 1996 as U.S. Pat. No. 5,555,276, which is acontinuation-in-part of U.S. application Ser. No. 07/735,128, filed Jul.22, 1991, now U.S. Pat. No. 5,365,546, which is itself acontinuation-in-part of U.S. application Ser. No. 07/467,096, filed Jan.18, 1990, now U.S. Pat. No. 5,052,020.

The U.S. application Ser. No. 08/279,148, filed Jul. 22,1994 and issuedAug. 12, 1997 as U.S. Pat. No. 5,657,317, is additionally acontinuation-in-part of U.S. application Ser. No. 08/275,821 filed Jun.10, 1994, now abandoned.

INCORPORATION BY REFERENCE

The above referenced applications, PCT Application No. PCT/US92/08610filed Oct. 1, 1992, as published under International Publication No. WO93/07691 on Apr. 15, 1993, together with U.S. Pat. No. 5,070,536, byMahany et al., U.S. Pat. No. 4,924,426, by Sojka, and U.S. Pat. No.4,910,794, by Mahany, are incorporated herein by reference in theirentirety, including drawings and appendices, and hereby are made a partof this application.

TECHNICAL FIELD

The present invention relates generally to local area networks used fortransmitting and receiving information and more particularly to asingular radio using multiple communication protocols for servicingcorresponding multiple radio local area networks.

BACKGROUND OF THE INVENTION

Multiple radio base station networks have been developed to overcome avariety of problems with single radio base station networks such asspanning physical radio wave penetration barriers, wasted transmissionpower by portable computing devices, etc. However, multiple radio basestation networks have their own inherent problems. For example, in amultiple base station network employing a single shared channel, eachbase station transmission is prone to collision with neighboring basestation transmissions in the overlapping coverage areas between the basestations. Therefore, it often proves undesirable for each base stationto use a single or common communication channel.

In contradistinction, to facilitate the roaming of portable or mobiledevices from one coverage area to another, use of a common communicationchannel for all of the base stations is convenient. A roaming device mayeasily move between coverage areas without loss of connectivity to thenetwork.

Such exemplary competing commonality factors have resulted in tradeoffdecisions in network design. These factors become even more significantwhen implementing a frequency hopping spread spectrum network. Frequencyhopping is a desirable transmission technique because of its ability tocombat frequency selective fading, avoid narrowband interference, andprovide multiple communications channels.

Again, however, changing operating parameters between coverage areascreates difficulties for the roaming devices which move therebetween. Inparticular, when different communication parameters are used, a portableor mobile device roaming into a new base station coverage area is notable to communicate with the new base station without obtaining andsynchronizing to the new parameters. This causes communication backlogin the network.

Moreover, even when a radio frequency network is established to coverthe premises of a building or group of buildings, certain types ofcommunication flow between certain types of devices make for inefficientuse of such a network. In fact, an ordinarily efficient networkconfiguration may be deemed intolerable in certain communicationscenarios.

Computer terminals and peripheral devices are widely used. Many types ofcomputer terminals exist which vary greatly in terms of function, powerand speed. Many different types of peripheral devices also exist, suchas printers, modems, graphics scanners, text scanners, code readers,magnetic card readers, external monitors, voice command interfaces,external storage devices, and so on.

Computer terminals have become dramatically smaller and more portable,as, for example, lap top computers and notebook computers. Computerterminals exist which are small enough to be mounted in a vehicle suchas a delivery truck or on a fork lift. Hand held computer terminalsexist which a user can carry in one hand and operate with the other.

Typical computer terminals must physically interface with peripheraldevices. Thus, there must either be a cable running from the computerterminal to each peripheral device, or the computer terminal must bedocked with the device while information transfer takes place.

In an office or work place setting, the physical connection is typicallydone with cables. These cables pose several problems. For example, manycables are required in order for a computer terminal to accommodate manyperipheral devices. In addition, placement of peripheral devices islimited by cable lengths. While longer cables may be used, they arecostly. Additionally, there may be a limited number of ports on acomputer terminal, thus limiting the number of peripherals that may beattached.

Another problem arises when several computer terminals must share thesame peripheral device, such as a printer. All of the computers must behardwired to the printer, which may create a protocol problem if thecomputer terminals are of different types.

Peripheral cabling is an even greater problem in scenarios wherehand-held and portable computer terminals are used. The cabling requiredfor an operator to carry a hand-held computer terminal in one hand, havea small portable printer attached to his belt, and carry a code readerin the other hand is cumbersome and potentially even dangerous. Forexample, such an operator loses a great deal of mobility and flexibilitywhile supporting a number of cabled devices. In addition, as cables wearout and break, exposed electric current could shock the operator, orcreate a spark and potentially cause a fire or explosion in some workareas.

The requirement of physically connecting the computer terminals andperipherals severely reduces the efficiency gained by making the devicessmaller. An operator must somehow account for all of the devices in asystem and keep them all connected. This can be very inconvenient. Forexample, an operator having a notebook computer and a modem in abriefcase may wish to have the freedom to move around with the computerbut without the modem. He may, for example, wish to work at variouslocations on a job sight and at various times transmit or receiveinformation via his modem. If the modem and the computer are hard wiredtogether, he must either carry the modem with him or keep connecting anddisconnecting it.

Furthermore, cabling can be expensive because cables frequently prove tobe unreliable and must be replaced frequently. In portable environments,cables are subject to frequent handling, temperature extremes, droppingand other physical trauma. It is not uncommon for the cables or theconnectors for the cables on the devices to need replacing every threemonths or so.

Attempts to alleviate or eliminate these problems have been made buthave not been entirely successful. One solution is to incorporate acomputer terminal and all of the peripherals into one unit. However,this solution proves unsatisfactory for several reasons. For example,the incorporation of many devices into one unit greatly increases thesize and weight of the unit, thus jeopardizing its portability.Furthermore, incorporating all of the functions into one unit greatlyreduces and, in most cases eliminates, the flexibility of the overallsystem. A user may only wish to use a hand-held computer terminal attimes, but at other times may also need to use a printer or occasionallya code reader. An all-incorporated unit thus becomes either overly largebecause it must include everything, or very limiting because it does notinclude everything.

Another solution has been to set up Local Area Networks (LAN's)utilizing various forms of RF (Radio Frequency) communication. The LAN'sto date, however, have been designed for large scale wirelesscommunications between several portable computer terminals and a hostcomputer. Therein, the host computer, itself generally a stationarydevice, manages a series of stationary peripherals that, upon requeststo the host, may be utilized by the portable terminals. Other largescale wireless communications have also been developed which provide forRF communication between several computer terminals and peripheraldevices, but have proven to be ineffective as an overall solution. Forexample, these systems require the peripheral devices to remain activeat all times to listen for an occasional communication. Although thisrequirement may be acceptable for stationary peripheral devicesreceiving virtually unlimited power (i.e., when plugged into an ACoutlet), it proves detrimental to portable peripherals by unnecessarilydraining battery power. Similarly, in such systems, the computerterminals are also required to remain active to receive an occasionalcommunication not only from the other terminals or the host, but alsofrom the peripherals. Again, often unnecessarily, battery power iswasted.

In addition, such large scale systems are designed for long range RFcommunication and often require either a licensed frequency or must beoperated using spread spectrum technology. Radios in such systems aretypically cost prohibitive, prove too large for convenient use withpersonal computers and small peripheral devices, and require a greatdeal of transmission energy utilization.

Furthermore, these systems do not provide for efficient communicationbetween portable computer devices and peripherals. For example, aportable computer device may be mounted in a delivery truck and a drivermay desire to transmit data to, or receive data from, a host computer orperipheral device at a remote warehouse location. While permitting suchtransmission, such wide area networks (WANs) only provide point-to-pointcommunications, use a narrow bandwidth, and often have heavycommunication traffic. As a result, WANs are generally slow andexpensive and simply do not provide an effective overall solution.

Additionally, in order for a computer device to be effectively portablein these systems, it must be capable of participating on any number ofLANs operating with different communication parameters and protocols.Thus, each portable computer device requires a plurality of built-inradio transceivers, one to accommodate each of such LANs. As a result,portable computer devices can become costly, excessively large, heavy,and power hungry.

Thus, there is a need for a radio frequency communication system andassociated radio that supports the use of network peripherals and solvesthe foregoing problems relating to power conservation and portability.

Another object of the invention is to provide a method and apparatuswherein collisions are minimized in overlapping coverage areas in amultiple base station network while providing a seamless communicationnetwork to support roaming devices.

Yet another object of the invention is to provide a method and apparatuswherein collisions are minimized in overlapping coverage areas byutilizing uncommon communication channel characteristics in a multiplebase station network, while still providing seamless communication forroaming devices by informing roaming devices of the nature of theneighboring base station communication channel characteristics.

A further object of the invention is to provide a communication networkwherein base stations communicate with roaming devices to help conservetransmission power usage.

A still further object of the present invention is to provide ahierarchical communications system utilizing spread spectrum frequencyhopping communication.

Other objects, advantages, and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention solves many of the foregoing problems in a varietyof embodiments. The network and associated radio of the presentinvention provides wireless peripheralization of roaming computingdevices and data collection devices. The roaming computing devicescommunicate over an extended area via a first local area network. Thefirst local area network is a high power radio communications system.Each mobile computer device can communicate with peripheral devices viaa second, low-power local area network. Additionally, the roamingcomputing device, also called the parent device, and peripherals maycommunicate within a limited area while moving within an independentwireless network that provides coverage over a much broader servicearea. Thus, the communications system comprises at least two independentwireless networks, with the parent device participating in the multiplenetworks by selectively processing and controlling the flow ofinformation among devices connected to the multiple networks.

In some embodiments, roaming computing or data collection devices andtheir peripherals communicate within a building or group of buildingsserviced by a wireless LAN, hereinafter called a premises LAN. Devicesthat are constituents of the premises LAN may also contain facilities(transceivers and protocols) for communicating with their peripheralsvia the separate low power, short range radio LAN, hereinafter aperipheral LAN or MicroLAN. The parent device contains significantprocessing power, such that information received from variousperipherals and other user input means, such as a keyboard attached tothe parent unit, is combined to form a message that is communicated overthe premises LAN. Information received from peripherals is selectivelycommunicated over the premises LAN in accordance with an applicationprogram, emulation mode, or operating system resident in the parentdevice.

Likewise, information received from the premises LAN may be processedand selectively forwarded to a peripheral. For example, a recordreceived through the premises LAN may be combined with informationobtained locally through another peripheral or user input means andprocessed by a local application to generate an invoice or shippingdocument that is then sent wirelessly to a portable printer peripheral.

The parent device may also enable communication among peripheral deviceswithin the peripheral LAN service area. Such communication may be eitherforwarded from source to destination peripherals through the parentdevice, or directly exchanged (peer to peer communications). The formeroccurs if the peripherals are within communication range of the parentbut not each other, or if other system design constraints, such as powermanagement dictate a centralized coordination function for powermanagement or data transfer efficiency.

The present invention is also capable of operation within radio WideArea Networks (WAN's). Vehicular based data communication is currentlyserviced by a variety of public and common carrier radio WAN's thatprovide connectivity to computer resources anywhere in the world, suchas RAM Mobile Data, ARDIS, MTEL, data PCS, CDPD, SMR, etc. The radioWAN's are generally bandwidth limited, and users are charged for serviceon the basis of the amount of data transferred. The hierarchical networkprovides means of connecting a premises LAN with a group of remotedevices via a radio WAN so as to minimize the expense and delays of suchradio WAN's.

For example, communication between a parent device or radio terminalmounted in a vehicle, hereinafter a "vehicle terminal", and hand-heldmobile terminal(s) that roam in an area local to the vehicle can becarried out using radio communication not subject to air time fees.Hereinafter, the network formed by the vehicle terminal and associatedhand-held terminal(s) is referred to as a "vehicular LAN".

The intelligence of the parent device, in the previous example a vehicleterminal, is key in processing information generated locally in thevehicular LAN and passing only essential information through the radioWAN to minimize cost of use. Information that is not time critical maybe selectively processed and stored for later batch downloading via thepremises LAN using hard-wired modems or wireless communication at adocking station located at a depot or central office.

The autonomous operation of the vehicular LAN allows it to continue tofunction when it is out of range of the WAN, when the WAN isinaccessible during peak usage periods, or when economics dictate thatWAN communication is unjustified.

The present invention relates generally to local area networks and, morespecifically, to a communication system for maintaining connectivitybetween devices on networks which have different operating parameterswhile limiting the power drain of battery powered devices.

In addition, a roaming computing device may have a single radio unitwhich has a control processor, memory, and a transceiver. Thetransceiver is capable of participating in at least a first and secondlocal area network which operate using a first and second communicationprotocol, respectively. The radio unit may participate as a slave to thefirst network pursuant to the first protocol and as a master to thesecond network pursuant to the second protocol, and the controlprocessor resolves conflicts between the first and second protocols.

In a further embodiment of the present invention, the control processorcauses the radio unit to enter a state of low power consumption when theradio unit is not communicating on either the first or second network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic illustration of a hierarchal communicationsystem built in accordance with the present invention.

FIG. 1B is a diagrammatic illustration of another hierarchalcommunication system built in accordance with the present invention.

FIG. 1C is a diagrammatic illustration of still another hierarchalcommunication system built in accordance with the present invention.

FIG. 2 illustrates an embodiment of a basic access interval structureused by a hierarchical network of the present invention.

FIGS. 3A and 3B illustrate the frequency of operation periodicallychanging corresponding to access interval boundaries in a frequencyhopping communication protocol of the present invention.

FIGS. 4A and 4B illustrate more than one access interval being used perhop in a frequency hopping communication protocol of the presentinvention.

FIG. 5A illustrates an embodiment of an access interval used by thehierarchical network of the present invention wherein a reservationphase is Idle Sense Multiple Access.

FIG. 5B illustrates an embodiment of an access interval used by thehierarchical network of the present invention wherein a device responsefollows a reservation poll.

FIG. 6A illustrates an embodiment of an access interval used by thehierarchical network of the present invention having multiplereservation slots for transmission of a Request For Poll signal.

FIG. 6B illustrates an embodiment of an access interval used by thehierarchical network of the present invention wherein general devicescontend for channel access.

FIG. 7A illustrates a sequence in an access interval used by thehierarchical network of the present invention for transferring data froma remote device to a control point device.

FIG. 7B illustrates a sequence in an access interval used by thehierarchical network of the present invention for transferring data froma control point device to a remote device.

FIG. 8 illustrates a preferred embodiment of an access interval used bythe hierarchical network of the present invention.

FIGS. 9A and 9B conceptually illustrate how multiple NETs may beemployed in an idealized cellular-type installation according to thepresent invention.

FIG. 10 illustrates a base station coverage contour overlap for themultiple NETs Infrastructured Network of FIG. 1.

FIG. 11 illustrates hopping sequence reuse in a multiple NETconfiguration of the present invention.

FIG. 12 illustrates a hierarchical infrastructured network of thepresent invention wherein a wireless link connects base stations onseparate hard wired LANs.

FIG. 13 illustrates a hierarchical infrastructured network of thepresent invention including a wireless base station.

FIG. 14 illustrates conceptually base stations communicating neighboringbase station information to facilitate roaming of portable/mobiledevices.

FIG. 15 illustrates a secondary access interval used in the MicroLAN orperipheral LAN in the hierarchical communication network according tothe present invention.

FIG. 16 is a flow chart illustrating the selection of a base station bya mobile computing device for communication exchange.

FIG. 17 is a flow chart illustrating a terminal maintainingsynchronization with the network after it has gone to sleep for severalaccess intervals.

FIG. 18 is a flow chart illustrating a terminal maintaining or achievingsynchronization with the network after it has gone to sleep for severalseconds.

FIGS. 19A and 19B are flow charts illustrating an access interval duringinbound communication.

FIGS. 20A and 20B are flow charts illustrating an access interval duringoutbound communication.

FIG. 21 illustrates a sequence in an access interval used in thehierarchical communication network of the present invention with TimeDivision Multiple Access slots positioned at the end of the accessinterval.

FIG. 22 illustrates a sequence in an access interval used by thehierarchical network of the present invention with the Time DivisionMultiple Access slots positioned immediately following the SYNC.

FIG. 23 illustrates a sequence in an access interval used by thehierarchical network of the present invention with the Time DivisionMultiple Access slots positioned immediately following the SYNC andReservation Poll.

FIG. 24 illustrates another sequence in an access interval used by thehierarchical network of the present invention with the Time DivisionMultiple Access slots positioned immediately following the SYNC.

FIG. 25 illustrates a portion of an access interval including thepreamble, SYNC and Reservation Poll.

FIG. 26 illustrates the information contained in a sample SYNC message.

FIG. 27 illustrates the information contained in a sample ReservationPoll.

FIG. 28a illustrates a warehouse environment incorporating acommunication network which maintains communication connectivity betweenthe various network devices according to the present invention.

FIG. 28b illustrates other features of the present invention in the useof a vehicular LAN which is capable of detaching from the premises LANwhen moving out of radio range of the premises LAN to perform a service,and reattaching to the premises LAN when moving within range toautomatically report on the services rendered.

FIG. 28c illustrate other features of the present invention in the useof a vehicular LAN which, when out of range of the premises LAN, isstill capable gaining access to the premises LAN via radio WANcommunication.

FIG. 29 is a diagrammatic illustration of the use of a peripheral LANsupporting roaming data collection by an operator according to thepresent invention.

FIG. 30 is a block diagram illustrating the functionality of RFtransceivers built in accordance with the present invention.

FIG. 31 is a diagrammatic illustration of an alternate embodiment of theperipheral LAN shown in FIG. 29.

FIG. 32 is a block diagram illustrating a channel access algorithm usedby peripheral LAN slave devices in accordance with the presentinvention.

FIG. 33a is a timing diagram of the protocol used according to thepresent invention illustrating a typical communication exchange betweena peripheral LAN master device having virtually unlimited powerresources and a peripheral LAN slave device.

FIG. 33b is a timing diagram of the protocol used according to thepresent invention illustrating a typical communication exchange betweena peripheral LAN master device having limited power resources and aperipheral LAN slave device.

FIG. 33c is also a timing diagram of the protocol used which illustratesa scenario wherein the peripheral LAN master device fails to service theperipheral LAN slave devices.

FIG. 34 is a timing diagram illustrating the peripheral LAN masterdevice's servicing of both the higher power portion of the premises LANas well as the lower power peripheral LAN subnetwork with a single orplural radio transceivers.

FIGS. 35 and 36 are block diagrams illustrating additional power savingfeatures according to the present invention wherein ranging and batteryparameters are used to optimally select the appropriate data rate andpower level of subsequent transmissions.

FIG. 37 illustrates an exemplary block diagram of a radio unit capableof current participation on multiple LANs according to the presentinvention.

FIG. 38 illustrates an exemplary functional layout of the frequencygenerator of FIG. 37 according to one embodiment of the presentinvention.

FIG. 39 illustrates further detail of the receiver RF processing circuitof FIG. 37 according to one embodiment of the present invention.

FIG. 40 illustrates further detail of the receiver signal processingcircuit of FIG. 37 according to one embodiment of the present invention.

FIG. 41 illustrates further detail of the receiver signal processingcircuit of FIG. 37 according to another embodiment of the presentinvention.

FIG. 42 illustrates further detail of the memory unit of FIG. 37according to one embodiment of the present invention.

FIG. 43 illustrates a software flow chart describing the operation ofthe control processor in controlling the battery powered radio unit toparticipate on multiple LANs.

FIG. 44 is an alternate embodiment of the software flow chart whereinthe control processor participates on a master LAN and, when needed, ona slave LAN.

FIG. 45 illustrates another embodiment of the communication system ofthe present invention as adapted for servicing a retail storeenvironment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a hierarchical communication system 10 within abuilding in accordance with the present invention. The illustratedhierarchical communication system 10 includes a local area network (LAN)for maintaining typical communication flow within the building premises,herein referred to as a premises LAN. The premises LAN is designed toprovide efficient end-to-end routing of information among hardwired andwireless, stationary and roaming devices located within the hierarchicalcommunication system 10.

The premises LAN consists of an infrastructure network comprising radiobase stations 15 and a data base server 16 which may be part of a moreextensive, wired LAN (not shown). The radio base stations 15 maycommunicate with each other via hard-wired links, such as Ethernet,RS232, etc., or via wireless (radio frequency) links. A plurality ofroaming terminal devices, such as a roaming computing device 20,participate in the premises LAN of the hierarchical communicationnetwork 10 to exchange information with: 1) other roaming computingdevices; 2) the data base server 16; 3) other devices which might beassociated with data base server 16 (not shown); and 4) any otherdevices accessible via the premises LAN (not shown). A roaming computingdevice can be, for example, a hand-held computer terminal or vehiclemounted computer terminal (vehicle terminal).

In most circumstances, the premises LAN provides a rather optimalsolution to the communication needs of a given network. However, in somecircumstances, to serve a variety of particular communication needs, thepremises LAN does not offer the optimal solution. Instead of relying onthe premises LAN for such communications, when and where beneficial,alternate LANs are spontaneously created by (or with) network devices,such as the roaming computing device 20, within the hierarchicalcommunication system 10. Such spontaneously created LANs are referred toherein as spontaneous LANs. After the immediate benefits end, i.e., atask has been completed, or if the participants of the spontaneous LANmove out of range of each other, the spontaneous LAN terminatesoperation.

An exemplary spontaneous LAN involves the use of peripheral devices asillustrated in FIG. 1A. Although bulk data transfer destined for aperipheral device 23, such as a printer, from the roaming computingdevice 20 might be communicated through the premises LAN, a more directinterconnection proves less intrusive, saves power, and offers a lowercost solution. Specifically, instead of communicating through thepremise LAN, the roaming computing device 20 needing to print: 1)identifies the presence of an available printer, the peripheral device23; 2) establishes an RF link (binds) with the peripheral device 23; 3)directly begins transferring the bulk data for printing; and 4) lastly,when the roaming terminal finishes the transfer, the spontaneous LANwith the peripheral device 23 terminates. A spontaneous LAN createdbetween the computing devices and peripheral devices is herein referredto as a peripheral LAN. Other types of spontaneous LANs, such asvehicular LANs, are also possible. Embodiments described below identifyvehicular LANs and wide area radio networks (WANs) which are part of thehierarchical communication system according to the present invention.

Although a spontaneous LAN may operate completely independent of thepremises LAN, it is more likely that there will be some degree ofcoordination between the two. For example, while participating in theperipheral LAN, the roaming computing device 20 may terminateparticipation in the premises LAN, and vice versa. Alternately, theroaming computing device 20 may only service the peripheral LAN whenspecific participation on the premises LAN is not required, or viceversa. Moreover, the roaming computing device 20 may attempt to serviceeach peripheral LAN as necessary in a balanced time-sharing fashion,placing little priority upon either LAN. Thus, based on the protocolsand hardware selected, a spontaneous LAN can be configured so as toexist hierarchically above, below, at the same level, or independent ofthe premises LAN.

In generally, to design a given LAN configuration, only thecharacteristics of that LAN are considered for optimization purposes.However, in the hierarchical communication system of the presentinvention, the operation of other LANs must also be taken into account.For example, because of the roaming computing devices participation inboth the premises and peripheral LANs, the requirements and operation ofthe premises LAN must be taken into consideration when defining theperipheral LAN, and vice versa. Thus, the hierarchical communicationsystem of the present invention provides a series of tightly coupledradio LANs and WANs with radio transceiver and communication protocoldesigns which take into consideration such factors as cost, weight,power conservation, channel loading, response times, interference,communication flow, etc., as modified by a primary factor of multipleparticipation.

The peripheral LAN replaces hard-wired connection between a roamingcomputing device and associated peripherals. In a typical configuration,a peripheral LAN will consist of one or more peripherals slaved to asingle master roaming computing device, although multiple master roamingcomputing devices are possible. Peripheral devices may be printers, codescanners, magnetic card readers, input stylus, etc.

Each of the peripheral devices 22 has a built-in radio transceiver tocommunicate with the roaming computing devices 20. The roaming computingdevices 20 are configured with built-in radio transceivers capable ofcommunicating on both the peripheral and premises LAN. The radio basestations 15 may be configured with radio transceivers only capable ofcommunicating in the premises LAN. In alternate embodiments, asdescribed below, the radio base stations 15 might instead be configuredto participate on both the premises and peripheral LANs.

In particular, the peripheral LAN is intended to provide communicationsbetween two or more devices operating within near proximity, e.g.,distances of a few tens of feet. The majority of constituents of theperipheral LAN are generally devices that do not require access toresources outside their immediate group, or which can suffice withindirect access through devices which participate outside theirimmediate peripheral LAN group. In contradistinction, the premises LANis intended to provide communications between relatively many devicesoperating across great distances throughout a building.

The characteristics of the peripheral LAN permit the use of radiotransceivers of lower cost, lower power consumption, and generally moresimplistic operation than permitted by the premises LAN. However, theoperation of the peripheral LAN is adapted for integration with thepremises LAN so that a radio transceiver and protocol designed foroperation on the premises LAN includes features which allow concurrentor sequentially concurrent operation on the peripheral LAN. For example,by selecting similar communication hardware characteristics andintegrating protocols, communication within the premises and peripheralLANs may be achieved with a single radio transceiver.

In one embodiment, radio communication through the premises LAN, i.e.,among the radio base stations 15 and the roaming computing device 20,utilizes relatively higher-power spread-spectrum frequency-hoppingcommunication with a reservation access protocol. The reservation accessprotocol facilitates frequency-hopping and supports adaptive data rateselection. Adaptive data rate selection is based upon the quality ofcommunication on the premises LAN radio channel. Radio communicationthrough the peripheral LAN utilizes a relatively lower-power singlefrequency communication also with a reservation access protocol. As morefully described below, the coordinated use of reservation accessprotocols in the peripheral and premises LANs maximize information flowwhile minimizing conflicts between devices participating in the twoLANs.

Referring to FIG. 1B, a small hierarchal communication system 30 builtin accordance with the present invention is shown. A base station 33 andtwo roaming or mobile computing devices 35 and 36 form a premises LAN37. The premises LAN 37 provides for communication among the mobilecomputing devices 35 and 36 and a host computer 34. The mobile computingdevices 35 and 36 can roam anywhere within the range of the base station33 and still communicate with the host computer 34 via the base station33.

Two peripheral LANs 40 and 41 allow for wireless communication betweeneach mobile computing device 35 and 36 and its respective peripheraldevices 43, 44 and 45 when the mobile computing device is notcommunicating on the premises LAN 37. Specifically, the peripheral LAN40 consists of the mobile computing device 35 and the peripheral device43, while the peripheral LAN 41 consists of the mobile computing device36 and the two peripheral devices 44 and 45.

FIG. 1C illustrates another embodiment according to the presentinvention of a larger hierarchal communication system 50. The hostcomputer 55 is connected to base stations 56, 57, 58 and 59. The hostcomputer 55 and the base stations 56, 57, 58 and 59 provide theinfrastructure for the premises LAN. The base stations need not behard-wired together. For example, as illustrated in FIG. 1C, the basestations 56, 57 and 58 access each other and the host computer 55 via ahard-wired link, while the base station 59 accomplishes such access viaa wireless link with the base station 58.

The base stations 56, 58 and 59 can support multiple mobile computingdevices. For example, the base station 56 uses a frequency-hoppingcommunication protocol for maintaining communication with mobilecomputing devices 61 and 62. Moreover, each of the mobile computingdevices may roam out of range of the base station with which they havebeen communicating and into the range of a base station with which theywill at least temporarily communicate. Together, the host computer 55and the base stations 56, 57, 58 and 59 and mobile computing devices 61,62, 64, 65 and 66 constitute a premises LAN.

More particularly, each base station operates with a different set ofcommunication parameters. For example, each base station may use adifferent frequency hopping sequence. Additionally, different basestations may not employ a common master clock and will not besynchronized so as to have the frequency hopping sequences start at thesame time.

Mobile computing devices 61, 62, 64, 65 and 66 are capable of roaminginto the vicinity of any of the base stations 56, 58 and 59 andconnecting thereto. For example, mobile computing device 62 may roaminto the coverage area of base station 58, disconnecting from basestation 56 and connecting to base station 58, without losingconnectivity with the premises LAN.

Each mobile computing device 61, 62, 64, 65 and 66 also participateswith associated peripherals in a peripheral LAN. Each peripheral LAN ismade up of the master device and its slave device. Similarly, asillustrated, the base station 57 is shown as a direct participant in notonly the premises LAN but also in the peripheral LAN. The base station57 may either have limited or full participation in the premises LAN.For example, the base station 57 may be configured as a mobile computingdevice with the full RF capability of transmission in both the premisesand peripheral LANs. Instead, however, participation in the premises LANmay be limited to communicating through the hard-wired link, effectivelydedicating the base station 57 to the task of servicing peripherals.

Although the use of a plurality of built-in radio transceivers could beused so as to permit simultaneous participation by a single device,factors of cost, size, power and weight make it desirable to onlybuild-in a single radio transceiver capable of multiple participation.Furthermore, even where a plurality of radio transceivers are built-in,simultaneous participation may not be possible depending upon thepotential transmission interference between transceivers. In fact, fullsimultaneous participation may not be desirable at least from aprocessing standpoint when one transceiver, servicing one LAN, always orusually takes precedence over the other. Justification for suchprecedence generally exists in a premises LAN over a peripheral LAN.

For example, communication flow in most premises LANs must be fast,efficient and rather robust when considering the multitude ofparticipants that operate thereon. In the peripheral LAN, however,response times and other transmission related delays are generally moreacceptable--even adding extra seconds to a peripheral printer's printtime will usually not bother the user. Thus, in such communicationenvironments, it may be desirable to design the transmitters andassociated protocols so that the premises LAN takes precedence over theperipheral LAN. This may yield a communication system where fullysimultaneous participation in both the premises and peripheral LANs doesnot exist.

In communication environments wherein fully simultaneous participationdoes not exist or is not desired, transmitter circuitry might be sharedfor participation in both the premises and peripheral LANs. Similarly,in such environments, the communication protocol for the peripheral LANcan be tightly coupled with the protocol for the premises LAN, i.e.,integrated protocols, so as to accommodate multiple participation.Moreover, one protocol might be designed to take precedence over theother. For example, the premises LAN protocol might be designed so as tominimize participation or response time in the peripheral LAN. Asdescribed in more detail below, such transceiver and protocol analysisalso takes place when considering additional multiple participation inthe vehicular LAN and WAN environments.

FIG. 2 illustrates an embodiment of a communication protocol for thepremises LAN which uses a basic Access Interval 200 ("AI") structureaccording to the present invention. Generally, an Access Interval is thebasic communication unit, a fixed block of time, that allocatesbandwidth to synchronization, media access, polled communications,contention based communications, and scheduled services. The AccessInterval in FIG. 2 includes a SYNC header 201 generated by a ControlPoint ("CP") device of a NET. The term NET describes a group of users ofa given hopping sequence or a hopping sequence itself. The Control Pointdevice is generally the base station 15 referenced above with regard toFIG. 1. The SYNC header 201 is used by constituents of the NET to attainand maintain hopping synchronization. A reservation phase 203 followspermitting a reservation poll, which provides the NET constituents anopportunity to gain access to media. A sessions frame 205 is nextallocated for communication protocol. A frame 207 follows for optionaltime division multiple access ("TDMA") slots in order to accommodatescheduled services. Scheduled services, for example, real time voice orslow scan video, are such that they require a dedicated time slot toprovide acceptable quality of service. The function of frames 201, 203,205 and 207 will be discussed in greater detail below.

As was shown in FIG. 2, FIG. 21 illustrates a sequence in an accessinterval 2100 with the Time Division Multiple Access slots 2113positioned at the end of the access interval 2100. In present example,if this were also a HELLO interval, the HELLO would immediately followthe SYNC 1201. Location of the Time Division Multiple Access slots atsuch a position provides certain advantages including, for example, 1)the SYNC 2101, HELLO (not shown), Reservation Poll 2103, may all becombined into a single transmission (concatenated frames); 2) hoppinginformation may be moved to or included in the Reservation Poll 2103allowing for a shorter preamble in the SYNC 2101; and 3) the HELLOmessages will occur early in the Access Interval 2100 providing forshorter receiver on times for sleeping terminals.

The Time Division Multiple Access slots may also be located at differentpoints within the access interval. Positioning the Time DivisionMultiple Access slots allow for various systemic advantages. Referringnow to FIG. 22, an access interval 2200 is illustrated showing the TimeDivision Multiple Access slots 2203 immediately following the SYNC 2201.Location of the Time Division Multiple Access slots 2203 at thisposition provides certain advantages including, for example, 1) bettertiming accuracy is achieved when the Time Division Multiple Access slots2203 immediately follow the SYNC 2201; 2) Session Overruns do notinterfere with the Time Division Multiple Access slots 2203; 3) deviceswhich do not use the Time Division Multiple Access slots 2203 do notnecessarily need to be informed of the Time Division Multiple Accessslot allocation; and 4) HELLO message may follow Time Division MultipleAccess slots 2203, Reservation Slots 2207 or Reservation Resolution Poll2209.

Referring now to FIG. 23, an access interval 2300 is illustrated showingthe Time Division Multiple Access slots 2305 immediately following theSYNC 2301 and the Reservation Poll 2303. In the present example, if thiswere a HELLO interval, a HELLO message would immediately follow theReservation Resolution Poll 2309.

Location of the Time Division Multiple Access slots 2305 at the positionshown in FIG. 23 provides certain advantages including, for example, 1)the Time Division Multiple Access slot timing is keyed to SYNC 2301 forbetter accuracy; 2) the number of Time Division Multiple Access slots2305 may be indicated in SYNC 2301 or the Reservation Poll 2303,providing greater flexibility; 3) Session frame overruns do notinterfere with Time Division Multiple Access slots 2305; 4) only onemaintenance transmission is required per Access Interval 2300; and 5)hopping information may be moved to or included in the Reservation Poll2303, permitting a shorter preamble in SYNC 2301.

In the access interval 2300 configuration shown in FIG. 23, it ispossible that the Time Division Multiple Access slots 2305 and theresponse slots 2307 could be the same. The Reservation Poll 2303 wouldallocate the correct number of slots and indicate which are reserved forTime Division Multiple Access. For example, to use Idle Sense MultipleAccess 1 slot) with 1 inbound and 1 outbound Time Division MultipleAccess slots, three slots would be allocated with the first two slotsreserved. The appropriate Time Division Multiple Access slot duration is80 bits at a hop rate of 200 hops per second which is just about theexpected duration of a Request for Poll. At slower hop rates, multipleslots could be allocated to Time Division Multiple Access allowing theTime Division Multiple Access slot duration to be constant regardless ofhop rate.

Referring now to FIG. 24, another access interval 2400 is illustratedshowing the Time Division Multiple Access slots 2403 immediatelyfollowing the SYNC 2401. In this example the Poll Message Queue 2405immediately follows the Time Division Multiple Access slots 2403. Theconfiguration shown in FIG. 24 provides for certain advantagesincluding, for example, 1) the Time Division Multiple Access slot timingis keyed to SYNC 2401 for better accuracy; and 2) Session frame overrunsdo not interfere with Time Division Multiple Access slots 2403.

The configurations shown in FIG. 21 and in FIG. 23 are preferred becausethey allow the Reservation Poll messages to be transmitted immediatelyfollowing the SYNC and because of the power management and interferencereduction advantages.

In one embodiment of the Access Interval structure, all messagetransmissions use standard high-level data link control ("HDLC") dataframing. Each message is delimited by High-Level Data Link ControlFlags, consisting of the binary string 01111110, at the beginning of themessage. A preamble, consisting of a known data pattern, precedes theinitial FLAG. This preamble is used to attain clock and bitsynchronization prior to start of data. Receiver antenna selection isalso made during the preamble for antenna diversity. A CRC for errordetection immediately precedes the ending FLAG. Data is NRZ-I(differentially) encoded to improve data clock recovery. High-Level DataLink Control NRZ-I data is run-length-limited to six consecutive bits ofthe same state. Alternatively, a shift register scrambler could beapplied instead of differential encoding to obtain sufficienttransitions for clock recovery. Data frames may be concatenated, withtwo or more frames sent during the same transmission, with a single FLAGseparating them. An example of this is SYNC, followed by a HELLO orReservation Poll (SYNC, HELLO and Reservation Poll are discussed morefully below).

While much of the following discussion centers on the use of frequencyhopping in the premises LAN, the Access Interval structure of thepresent invention is also suitable for single channel and directsequence spread spectrum systems. The consistent timing of channelaccess, and the relative freedom from collisions due to channelcontention, provide desirable benefits in systems that support portable,battery powered devices regardless of modulation type or channelization.Functions that are unique to frequency hopping may be omitted if otherchannelization approaches are used.

FIGS. 3a and 3b illustrate the frequency of operation periodicallychanging corresponding to Access Interval boundaries in a frequencyhopping system. Frequency hopping systems use a hopping sequence, whichis a repeating list of frequencies of length (n) selected in a pseudorandom order and is known to all devices within a coverage area. FIG. 3aillustrates a frequency hopping system having one Access Interval 301per frequency hop (the hop occurring every 10 milliseconds) and a lengthof 79. FIG. 3b illustrates a frequency hopping system having one AccessInterval 303 per frequency hop (the hop occurring every 20 milliseconds)and a length of 79. The 20 ms time frame is preferred for a protocolstack that uses a maximum network layer frame of up to 1536 bytespayload while maintaining two real time voice communications channels.Access interval duration may be optimized for other conditions. AccessInterval length is communicated to the NET during the SYNC portion ofthe Access Interval. This allows Access Interval duration, and other NETparameters to be adjusted without reprogramming every device within theNET.

The Access Interval is a building block. The length of the AccessInterval can be optimized based on network layer packet size, expectedmix of Bandwidth on Demand ("BWOD") and Scheduled Access traffic,expected velocities of devices within the NET, acceptable duration ofchannel outages, latency or delay for scheduled services, etc. Thepreferred Access Interval duration of 20 ms (and maximum packet lengthof 256 Bytes at 1 MBIT/sec) represents a value chosen for systems withdevice velocities up to 15 MPH, and a mix between Bandwidth On Demandand scheduled service traffic.

Within a frequency hopping network, one or more Access Intervals may beused during each dwell in a frequency hopping system. A dwell is thelength of time (d) each frequency in the hopping sequence is occupied bythe system. For example, FIGS. 4a and 4b show illustrations of caseswhere more than one 20 ms Access Interval 401 is used per hop. This maybe appropriate for some instances where it is undesirable to hop athigher rates because of relatively long frequency switching times of theradio hardware, where import, export, or regulatory restrictionsdisallow hopping at a faster rate, or in some applications where it isdesirable to maintain operation on each channel for a longer period. Anexample of the latter is the case where larger files or data records aretransferred routinely.

In a frequency hopping operation, the Access Interval 200 of FIG. 2begins with a SYNC header 201. As mentioned above, the SYNC is generatedby the Control Point (CP) device of the NET. The SYNC is used byconstituents of the NET to attain and maintain hopping synchronization.Included in the SYNC are:

1. Address of the Control Point device.

2. Identification of the Hopping Sequence, and index of the currentfrequency within the hop table.

3. Identification of the hop rate, number of Access Intervals per hop,and Access Intervals before next hop.

4. A timing character for synchronization of device local clocks to theNET clock contained within the Control Point device.

5. Status field indicating reduced SYNC transmissions due to low NETactivity (Priority SYNC Indicator).

6. Status field indicating if the Access Interval will contain abroadcast message to all devices within the NET.

7. Status field indicating premises or spontaneous LAN operation.

8. The SYNC field information is optionally encrypted using a blockencryption algorithm, with a key provided by the network user. A randomcharacter is added to each SYNC message to provide scrambling.

However, there are two circumstances during which a SYNC message is nottransmitted: 1) co-channel interference; and 2) low NET utilization.With regard to co-channel interference, before issuing a SYNC message,the Control Point device performs channel monitoring for a briefinterval. If the Received Signal Strength Indicator (RSSI) levelindicates an ON channel signal greater than the system defer threshold,then the Access Interval is skipped. Alternatively, a strong ON channelsignal may dictate a reduction in Control Point device power to limitthe interference distance of the net for the duration of the AccessInterval. A system defer threshold 30 dB above the receiver sensitivityis a preferred choice. Communication within the NET is deferred for theduration of the Access Interval if SYNC is not transmitted due toco-channel interference.

In times of low system utilization, SYNC and Reservation Poll messagesare reduced to every third Access Interval. The SYNC message includes astatus field indicating this mode of operation. This allows devices toaccess the NET, even during Access Intervals where SYNC is skipped, byusing an Implicit Idle Sense algorithm. If the hopping sequence is 79frequencies in length as shown in FIGS. 3a and 3b, use of every thirdAccess Interval guarantees that a SYNC message will be transmitted oneach frequency within the hopping sequence once each three cycles of thesequence, regardless of whether 1, 2 or 4 Access Intervals occur eachhop dwell. This addresses US and European regulatory requirements foruniform channel occupancy, and improves the prospects forsynchronization of new units coming into the NET during periods when theNET is otherwise inactive. SYNC messages that are on multiples of 3Access intervals are labeled as priority SYNC messages. "Sleeping"terminals use priority SYNCs to manage their internal sleep algorithms.Sleeping terminals and Implicit Idle Sense are discussed in more detailbelow.

It should be noted that SYNC messages are preceded by dead time, whichmust be allocated to account for timing uncertainty between NET clocksand local clocks within NET constituents. In frequency hopping systems,the dead time must also include frequency switching time for the RFmodem.

The Reservation Poll frame 203 immediately follows the SYNC header 201.The two messages are concatenated High-Level Data Link Control framesseparated by one or more Flags. The reservation poll provides NETconstituents an opportunity to gain access to the media. It includes:

1. A field specifying one or more access slots.

2. A field specifying a probability factor between 0 and 1.

3. A list of addresses for which the base stations has pending messagesin queue.

4. Allocation of Time Division Multiple Access slots for scheduledservices by address.

5. Control Point device Transmitted Power level for SYNC and ReservationPolls.

The number of access slots, n, and the access probability factor, p, areused by the Control Point device to manage contention on the channel.They may each be increased or decreased from Access Interval to AccessInterval to optimize access opportunity versus overhead.

If the NET is lightly loaded, the pending message list is short, and theNET is not subject to significant interference from other nearby NETS,the control point device will generally specify a single slot 501 asshown in FIG. 5a, with a p factor <1. In this case, the reservationphase is Idle Sense Multiple Access ("ISMA"). Devices with transmissionrequirements that successfully detect the Reservation Poll will transmita Request for Poll ("RFP") with probability p and defer transmissionwith probability 1-p. FIG. 5b shows a device response (address 65 503following the reservation poll.

In cases when the transmission density is higher, n multiple reservationslots will be specified, generally with a probability factor p of 1. Inthis case a device will randomly choose one of n slots for transmissionof their Request for Poll. The slotted reservation approach isparticularly appropriate in instances where many NETs are operating innear proximity, since it diminishes reliance on listen before talk("LBT") (explained more fully below). The number of slots n isdetermined by a slot allocation algorithm that allocates additionalslots as system loading increases. FIG. 6a shows multiple slots 601.

In cases where NET loading is extreme, the Control Point may indicate anumber of slots, e.g., not more than 6, and a probability less than 1.This will cause some number of devices to defer responding with aRequest for Poll in any of the slots. This prevents the control pointdevice from introducing the overhead of a large number of slots inresponse to heavy demand for communications, by dictating that someunits back off until demand diminishes.

A pending message list is included in the Reservation Poll. The pendingmessage list includes the addresses of devices for which the ControlPoint device has messages in queue. Devices receiving their address maycontend for the channel by responding with a Request For Poll (RFP) inthe slot response phase. FIG. 6b shows several devices 603, 605 and 607contending for channel access. Messages that the Control Point devicereceives through the wired infrastructure that are destined for Type 1devices, and inactive Type 3 devices whose awake window has expired, areimmediately buffered, and the device addresses are added to the pendingmessage list. When a message is received through the infrastructure fora Type 2 device, or an active Type 3 device, their address isprioritized at the top of the polling queue. (Device Types and pollingqueue are described below.) The pending message list is aged over aperiod of several seconds. If pending messages are not accessed withinthis period, they are dropped.

Devices with transmission requirements respond in slots with a Requestfor Poll. This message type includes the addresses of the Control Pointdevice and requesting device, the type and length of the message it hasto transmit, and a field that identifies the type of device. Devicesthat detect their address in the pending message list also contend foraccess in this manner.

As mentioned above, devices may be Type 1, Type 2, or Type 3. Type 1devices are those which require critical battery management. These maybe in a power saving, non-operational mode much of the time, onlyoccasionally "waking" to receive sufficient numbers of SYNC andReservation Poll messages to maintain connectivity to the NET. Type 2devices are those that are typically powered up and monitoring the NETat all times. Type 3 units are devices that will remain awake for awindow period following their last transmission in anticipation of aresponse. Other device types employing different power managementschemes may be added.

Slot responses are subject to collision in both the single and multipleslot cases. Collisions may occur when two or more devices attempt tosend Request for Polls in the same slot. However, if the signal strengthof one device is significantly stronger than the others, it is likely tocapture the slot, and be serviced as if it were the only respondingunit. FIG. 6b shows two devices 605, address 111, and 607, address 02,that may be subject to collision or capture.

The Control Point device may or may not be able to detect collisions bydetecting evidence of recovered clock or data in a slot, or by detectingan increase in RF energy in the receiver (using the Received SignalStrength Indicator, ("RSSI")) corresponding to the slot interval.Collision detection is used in the slot allocation algorithm fordetermining addition or deletion of slots in upcoming Reservation Polls.

As an optional feature to improve collision detection in the multipleslot case, devices that respond in later slots may transmit theaddresses of devices they detect in earlier slots as part of theirRequest for Poll. Request for Polls which result in collisions at theControl Point device often are captured at other remote devices, sincethe spatial relationship between devices that created the collision atthe base does not exist for other device locations within the NET. Theduration of the response slots must be increased slightly to providethis capability.

If the Control Point device receives one or more valid Request for Pollsfollowing a Reservation Poll, it issues a Reservation Resolution ("RR")Poll and places the addresses of the identified devices in a pollingqueue. The Reservation Resolution message also serves as a poll of thefirst unit in the queue. Addresses from previous Access Intervals andaddresses of intended recipients of outbound messages are also in thequeue.

If the Polling Queue is empty, then no valid Request for Polls werereceived or collision detected and no Reservation Resolution poll isissued. If within this scenario a collision is detected, a CLEAR messageindicating an Explicit Idle Sense (explained more fully below) istransmitted containing a reduced probability factor to allow collidingunits to immediately reattempt NET access.

Outbound messages obtained through the network infrastructure may resultin recipient addresses being prioritized in the queue, that is, if therecipients are active devices--Type 2 devices or Type 3 devices whoseawake window has not expired. This eliminates the need for channelcontention for many outbound messages, improving efficiency. Messagesfor Type 1 devices are buffered, and the recipient address is placed inthe pending message list for the next Access Interval.

Generally the queue is polled on a first in first out (FIFO) basis. Thepolling order is:

a. Addresses of active units with outbound messages.

b. Addresses from previous Access Intervals

c. Addresses from the current Access Interval

Since propagation characteristics vary with time and operatingfrequency, it is counterproductive to attempt retries if Poll responsesare not received. If a response to a Poll is not received, the nextaddress in the queue is polled after a short response time-out period.Addresses of unsuccessful Polls remain in the queue for Polling duringthe next Access Interval. Addresses are aged, so that after severalunsuccessful Polls they are dropped from the queue. Addresses linked tooutbound messages are added to the pending message list. Devices withinbound requirements must re-enter the queue through the nextreservation phase.

Data is transferred in fragments. A maximum fragment payload of 256bytes is used in the preferred implementation. If transfer of networkpackets larger than of 256 bytes is required, two or more fragments aretransferred. Fragments may be any length up to the maximum, eliminatingthe inefficiency that results when messages that are not integermultiples of the fragment length are transmitted in systems that employfixed sizes.

The sequence for transferring data from a remote device to the controlpoint device is illustrated in FIG. 7a. It is assumed that address 65 isthe first address in the polling queue. The Reservation Resolution poll701 from the control point device includes the device address and themessage length that device 65 provided in its initial Request for Poll.A first fragment 703 transmitted back from device 65 is a full lengthfragment. Its header includes a fragment identifier and a fieldproviding indication of the total length of the message. Lengthinformation is included in most message types during the sessions periodto provide reservation information to devices that may wish to attemptto access the NET following an Explicit Idle Sense (explained more fullybelow).

Following successful receipt of the first fragment, the Control Pointdevice sends a second poll 705, which both acknowledges the firstfragment, and initiates transmission of the second. The length parameteris decremented to reflect that the time required for completion of themessage transfer is reduced. A second fragment 707 is transmitted inresponse, and also contains a decremented length field. Followingreceipt of the second fragment 707, the Control Point device sends athird poll 709. This pattern is continued until a final fragment 711containing an End of Data (EOD) indication is received. In FIG. 7, thefinal fragment is shorter than a maximum length fragment. The ControlPoint device sends a final Acknowledge (ACK), and the device sends afinal CLEAR 713 to indicate conclusion of the transmission. The CLEARmessage contains a probability factor p for Explicit Idle Sense(explained more fully below). The value of p is determined by theControl Point device in the ACK and echoed by the device terminationcommunication. A p of zero indicates that the control point device willbe initiating other communications immediately following receipt of theCLEAR message. A probability other than 0 indicates an Explicit IdleSense.

If for some reason a fragment is not successfully received, the nextpoll from the Control Point device would indicate a REJECT, and requestre-transmission of the same fragment. The length field would remainfixed at the previous value, prolonging reservation of the channel forthe duration of the message. After a fragment is transmitted more thanonce without successful reception, the Control Point device may suspendattempts to communicate with the device based upon a retry limit, andbegin polling of the next address in the queue.

A flow chart depicting how inbound messages are received during anaccess interval is shown in FIGS. 19A and 19B. A flow chart depictinghow outbound messages are transmitted during an access interval is shownin FIGS. 20A and 20B.

Outbound messages are transmitted in a similar fashion as inboundmessages, with the Control Point and device roles largely reversed asillustrated in FIG. 7b. When the Control Point reaches an address in thequeue for which it has an outbound message, the Control Point transmitsa Request for Poll 721 identifying the address of the device and thelength of the message. The response back from the device would be a pollwith an embedded length field. The same POLL/FRAGMENT/ACK/CLEARstructure and retry mechanisms as described above with regard to inboundmessages in reference to FIG. 7a are maintained. The CLEAR from thedevice indicates a probability p of zero. If the polling queue is empty,the Control Point may send a final or terminating CLEAR 723 containing aprobability for Explicit Idle Sense.

All terminating ACK or CLEAR messages contain fields to aid insynchronization of new units to the NET. The content of these fields isidentical to that in the SYNC message, except that the timing characteris deleted. Synchronization is discussed more fully below.

Broadcast Messages intended for groups of addresses, or all addresseswithin a NET may be transmitted during the sessions period. Broadcastmessages are not individually acknowledged. These messages may becommunicated at intervals over the course of several Access Intervals toprovide reliable communication. Messages such as SYNC and ReservationPolls are specialized broadcast messages, with dedicated bandwidth inthe Access Interval structure.

Security of payload data is left to the higher protocol layers.Application programs resident in portable/mobile devices may employencryption or other means of providing protection against undesired useof transmitted data.

Portable/mobile devices may employ transmitter power control during thesessions period to reduce potential interference with other NETs thatmay occasionally be on the same or adjacent channels. These devices willuse Received Signal Strength Indicator readings from outbound messagesto determine if transmitter power may be reduced for their inboundtransmission. Because of the need to maintain channel reservations andListen Before Talk capabilities, the Control Point device does not usetransmitter power control. Since Control Point devices are generallypart of an installed system infrastructure, they are likely to bephysically separated from devices operating in other NETs. They aretherefore less likely to cause interference to devices in other NETsthan portable devices, which may operate in proximity to devices inother NETs.

Often, control point devices will empty the polling queue before theconclusion of the access interval. Two mechanisms within the AccessControl Protocol, Explicit and Implicit Idle Sense, are provided toimprove bandwidth utilization. These supplemental access mechanismsoften provide means for devices that failed to gain reservations duringthe reservation phase to gain access to the NET within the AccessInterval. To assume an Explicit or Implicit Idle Sense, a device musthave detected a valid SYNC and Reservation Poll in the current AccessInterval.

The incorporation of a probability factor p≠0 in the final (terminating)ACK or CLEAR from the control point device provides the function of anExplicit Idle Sense (mentioned above). Devices with transmissionrequirements solicit Request for Polls using the same rules normallyused for a single slot Reservation Poll. Successfully identifiedaddresses are placed in the polling queue, and are polled immediately orin the next Access Interval depending on the time remaining in thecurrent Access Interval. The p factor for Explicit Idle Sense is subjectto the same optimization algorithm as the Reservation Poll probability.

Communication of channel reservations, in the form of the length fieldsin Polls and Message Fragments is useful to units seeking to access theNET through Explicit Idle Sense. Reservations allow devices topredictably power down during the period that another device hasreserved the NET to conserve battery power, without loosing the abilityto gain access to the NET.

Implicit Idle Sense provides an additional means of channel access. AnImplicit Idle Sense is assumed whenever a device detects a quietinterval period greater than or equal to the duration of a Poll plus themaximum fragment length after a channel reservation has expired.Detection based upon simple physical metrics, such as a change inReceived Signal Strength Indicator or lack of receiver clock recoveryduring the quiet interval, are preferred methods of ascertaining channelactivity. Algorithms based upon these types of indicators are generallyless likely to provide a false indication of an inactive channel thanthose that require successful decoding of transmissions to determinechannel activity. False invocation of an Implicit Idle Sense is the onlymechanism by which data transmissions are subject to collision withinthe NET. Thus, the Implicit Algorithm must be conservative.

Quiet interval sensing may begin at the following times within theAccess Interval:

a. Any time after the last reservation slot following a ReservationPoll;

b. Any time after a terminating ACK or CLEAR indicating an Explicit IdleSense;

c. Following an unsuccessful response to a single Slot Reservation Poll;or

d. Any time prior to reserved Time Division Multiple Access time slotsat the end of the Access Interval.

It is preferable that devices detecting a quiet interval use a ppersistent algorithm for channel access to avoid collisions. Theprobability factor for Implicit Idle Sense Access will generally be lessthan or equal to the factor in Explicit Idle Sense.

A device must receive the SYNC and Reservation Polls at the beginning ofan Access Interval to use Implicit Idle Sense. The Reservation Pollprovides indication of guaranteed bandwidth allocation to scheduledservices at the end of the Access Interval, which may shorten the periodavailable for Bandwidth On Demand communications.

Devices requiring scheduled services must contend for the channel in thesame fashion as those requiring Bandwidth On Demand access. When polled,these initiating devices will initiate a connection request thatindicates the number of inbound and outbound Time Division MultipleAccess slots required for communication, and the address of the targetdevice with which communication is desired. The network infrastructurewill then attempt to establish the connection to the target device. Oncethe connection is established, the Control Point device will signal theallocation of slots to the initiating device. Time Division MultipleAccess slots are relinquished by transmitting a disconnect message tothe control point device in the Time Division Multiple Access slot untilthe disconnect is confirmed in the next Reservation Poll.

The transmission requirements of speech and slow scan video (scheduledservices) are similar. In one embodiment, Time Division Multiple Accessslots are allocated as multiples of 160 bits payload at 1 MBIT/sec, plusoverhead for a total of 300 μs. For 10 ms access intervals, acceptablevoice communication can be obtained by allocating 1 Time DivisionMultiple Access slot each for inbound and outbound communication peraccess interval. For 20 ms access intervals, two slots each way arerequired. A system employing 10 ms access intervals at 100 hops persecond may improve transmission quality by using two or three slots eachAccess Interval and sending information redundantly over two or threeaccess intervals using interleaved block codes. Scheduled transmissionsare generally not subject to processing or validation by the controlpoint device, and are passed through from source to destination. Use ofinterleaved error correction coding or other measures to improvereliability are transparent to the NET.

The selection of certain system parameters are important whenconsidering scheduled services. As an example, since speech is quantizedover the duration of the access interval and transmitted as a burst, thelength of the access interval translates directly into a transport delayperceptible to the recipient of that speech. In real time voicecommunications, delays longer than 20 ms are perceptible, and delayslonger than 30 ms may be unacceptable. This is particularly the casewhere the premises LAN is interconnected with the public switchedtelephone network ("PSTN"), which introduces its own delays. Two wayservices such as voice communications are the most sensitive totransport delay because delay impacts the interaction of thecommunicating parties. One way services are less sensitive to transportdelay. One way services are good candidates for interleaving or otherforms of redundant transmission.

Similarly, the selection of hop rate is important, as hop ratedetermines the duration of outages that may occur. If one or morefrequencies in the hop sequence are subject to interference, forinstance, scheduled transmissions during those hops will be disrupted.In a system that hops slowly, detrimental outages of hundreds ofmilliseconds will occur resulting in poor transmission quality.Occasional losses of smaller durations, e.g., 10 ms or 20 ms, aregenerally less perceptible, indicating that faster hop rates aredesirable if the NET is to offer real time voice transport.

Scheduled service intervals may also be used for data transport on ascheduled or priority basis. Telemetry, data logging, print spooling,modem replacement, or other functions are possible. For theseactivities, a few Time Division Multiple Access slots scheduled forexample every fourth, eighth, or sixteenth Al are necessary.

Because of multipath and dispersion issues with 2.4 GHz transmission atrelatively high data rates, the ability of the NET to adaptively switchbetween two or more data rates is desirable.

In one embodiment, implementation of data rate switching may beaccomplished by selecting a standard rate of communications, e.g., 250KBPS and high rate of communications of 1 Mbit/sec. Messages thatcontain system status information, including SYNC, Reservation Polls,Reservation Resolution Polls (Request for Polls), Polls, ACKs and CLEARSare transmitted at the standard rate. These messages are generallyshort, and the time required for transmission is largely determined byhardware overhead, e.g., transmitter receiver switching time. Theincremental overhead introduced by transmitting these messages at thelower rate is therefore small in comparison to the total length of anaccess interval. The reliability of reception of these messages willincrease, which will eliminate unnecessary retries in some instanceswhere fragments are received successfully,. but acknowledgements orpolls are missed.

A test pattern at the higher data rate is inserted in each Poll (not inReservation Polls, however). The Poll recipient evaluates signal qualitybased on the high data rate test pattern, Received Signal StrengthIndicator, and other parameters to determine whether to transmit afragment at the high rate or the low rate. Fragment lengths are selectedsuch that high and low rate maximum fragment lengths are the sameduration. In other words, a fragment at the low rate conveysapproximately 1/4 the payload of a fragment for the case where the datarate is four time greater. This method is generally suitable fortransaction oriented communications, which frequently require shortmessage transmissions. Alternatively, the length field in Polls andmessages can be used to allow different fragment lengths for the twodata rates while still providing channel reservation information toother devices in the NET. This method also provides for forwardmigration. As modulation and demodulation methods improve, newerproducts can be added to old networks by upgrading Control Pointsdevices. Both new and old devices share the ability to communicate at acommon low data rate.

An alternate embodiment uses signaling messages such as SYNC,Reservation Polls, Request for Polls, etc., at the higher rate withfallback operation to the standard rate for the communications sessionsonly. SYNC and Reservation Polls at the high rate constitute a high datarate test message. The Request for Poll response to the Reservation Pollat the high rate may include a field indicating that sessionscommunications should take place at the fallback, standard rate. Signalquality measures such as signal strength and clock jitter areappropriate. Data rate selection information is included with the deviceaddress in the polling queue. When the device is polled, it will bepolled at the rate indicated in the Request for Poll. Channelreservation information in the Reservation Resolution Poll will indicatethe reservation duration based upon the data rate indicated.

In this alternate embodiment, the fact that SYNC and Reservation Pollsmust be detectable at the high data rate prioritizes access to the NETfor those devices that have acceptable connectivity during the currentaccess interval. This general approach has desirable characteristics ina frequency hopping system, as the propagation characteristics betweendevices may change significantly as the NET changes from frequency tofrequency within the hopping sequence, or over several Access Intervalsduring the dwell time on a single frequency. Reduction in data rate inthis system is primarily intended to remedy the data smearing(intersymbol interference) effects of dispersion due to excess delay,rather than temporary poor signal to noise ratio due to frequencyselective fading. Devices that receive high data rate transmissions withacceptable signal strength but high jitter are likely to be experiencingthe effect of dispersion.

The concept of allowing Polls and message fragments to occur at either ahigh or low data rate could create difficulties for other NETconstituents that need to be able to monitor the channel for reservationinformation. Two embodiments for solving this problem are the use ofauto-discriminating receivers or the use of fixed data rate headers forsystem communications.

Auto discrimination requires the receiver to process messages sent ateither data rate, without necessarily having prior knowledge of therate.

Given a high rate of 1 MBIT/SEC, and a low Rate of 250 KBPS, i.e., onebeing a binary multiple of the other, it is possible to devise preamblesthat can be received at either rate. Consider that 01 and 110 sent atthe low rate correspond to 00001111 and 111111110000 at the high rate.These preambles are transmitted continuously before the transmission ofthe High-Level Data Link Control FLAG character at the correct data rateindicating the start of a message. In this example, a preamble of 20bits of 01 at the low rate indicates operation at the high rate. Apreamble of 30 bits of 110 indicates operation at the low rate. Areceiver tuned to either rate is capable of receiving both types ofpreambles and initiating the proper decoding mechanisms for the intendedrate of transmission.

This general technique, with appropriate selection of preamble content,is applicable to binary modulation schemes, for example, a frequencymodulated system where a common frequency deviation value is used forboth data rates. It is also applicable to systems where switching occursbetween binary and multilevel modulation, such as disclosed in pendingU.S. application Ser. No. 07/910,865, filed Jul. 6, 1992.

Referring now to FIG. 25, a preamble 2501, a SYNC 2503 and a ReservationPoll 2505 is illustrated. The preamble 2501 starts at the beginning ofthe Access Interval 2500 and is applied to an RF modem while it isswitching frequencies. Since the switching time is a worst case, thiscauses the preamble 2501 to be present and detectable prior to theallocated 150 μsec period in some instances. It would be equallyappropriate to begin preamble transmission 50 or 100 μsec into theswitching period if that would be more convenient. The timing has beenselected to allow 100 μsec.

Referring to FIG. 26, a sample SYNC message 2600 is shown. Referring toFIG. 27, a sample Reservation Poll 2700 is shown. In these examples, thehopping synchronization information has been positioned in theReservation Poll 2700.

With auto-discrimination, it is possible to change data rates on aper-poll basis, thereby adjusting for channel temporal dynamics. Sinceall devices in the NET have auto discrimination capabilities, andchannel reservation information is included in message headers as alength field, the bandwidth reservation features of the NET arepreserved. The maximum fragment duration may be maintained at a fixedvalue, meaning that low data rate fragments convey less data than theirhigh rate counterparts, or may be scaled in the ratio of the data ratesto allow consistent fragment data payloads.

An alternative to auto-discrimination is the use of headers tocommunicate system information. This embodiment is less preferred, butmay be appropriate if economics, size, or power constraints dictate asimpler design than that required for auto-discrimination. In thisembodiment, any transmission at the lower data rate is preceded by aheader at the high data rate that conveys NET management information,i.e., channel reservation status. Devices other than those directlyinvolved in polling or fragment transmission need only monitor at thehigh rate for channel reservation information. The header at the highrate and the following transmission at the low rate are concatenatedHigh-Level Data Link Control frames, with an appropriate preamble forlow rate clock recovery synchronization inbetween.

For the communicating devices, the header can serve the additionalpurpose of acting as a test pattern at the high rate. For example, if adevice is polled at the low rate, but successfully decodes the high rateheader with adequate signal quality, it may indicate back to the pollingunit to poll again at the high rate.

In a premises LAN as discussed in reference to FIG. 1, many NETs may bedistributed geographically to provide enhanced coverage or additionalsystem capacity. The wired portion of the network infrastructure, suchas Ethernet or Token Ring, provides a means for coordination of NETs toachieve optimum system performance. An equally important role of thewired infrastructure is to allow resource sharing. Portable devices withlimited memory capacities, processing power, and relatively smallbatteries may access large data bases on, or remotely initiateprocessing capabilities of, larger AC powered computer systems.Portable/mobile devices may also share communication with other likedevices which are serviced by other NETs well beyond the radio coveragerange of their own NET.

The basic method for communication of status information regarding thepremises LAN is the HELLO message. HELLO messages are sent routinely,but relatively infrequently, for example, every 90 Access Intervals. TheHELLO transmission interval is tied to the Priority SYNC interval, sothat the HELLO interval corresponds to Access Intervals where SYNC istransmitted if the network is lightly utilized.

In an alternate embodiment, HELLOs could be inserted as a broadcastmessage at the beginning of the Sessions period. FIG. 8 illustrates apreferred Access Interval embodiment where a HELLO message 801 isinserted between a SYNC 803 and a Reservation Poll 805. The SYNC frameat the beginning of the Access Interval indicates that the AccessInterval will contain a HELLO, allowing power managed devices to remainawake to receive the HELLO.

HELLO messages may also contain information regarding pending changes inthe local NET. If the local NET is changing Access Interval durations orhop sequences, for instance, changes may be communicated in severalconsecutive HELLOs so that the information is reliably communicated toall NET constituents, permitting all devices to make the change incoordinated fashion. Further discussion of HELLO message content isprovided below.

For purposes of channel management in the Access Interval structure, themaximum transmission duration by a device should be limited to the timethat the device moving at a maximum expected velocity can traverse 1/4wavelength of the maximum carrier frequency. The duration may be furtherreduced to compensate for link bit error rate characteristics orexpected duration or frequency of interference bursts. A maximumtransmission duration of 2.5 ms is suitable for 1 MBIT/SEC transmission,with a device velocity of 15 mph, in a multiple NET environment.

Use of spatial or polarization antenna selection diversity is alsodesirable in indoor propagation environments. First, the receiving unitmakes an antenna diversity decision during the preamble portion of eachtransmission. The antenna used for reception for each device address isthen recorded in memory so that the correct antenna will be used forresponse messages to each address. While diversity selection is onlyvalid for a short time, it is not necessary to age this information,because antenna selection is equi-probable even after diversityinformation is no longer valid.

The Access Interval structure of the present invention also inherentlyprovides routine channel sounding for each hop. This is important in afrequency hopping system, as channel conditions will vary considerablyfrom frequency to frequency within the hopping sequence. NETconstituents must, in most cases, be able to receive SYNC andReservation Poll transmissions from the Control Point device to attemptinbound access in an Access Interval. This provides a positiveindication that the device is not experiencing a channel outage,allowing power saving and eliminating possible channel contention.Channel sounding does not need to be employed during periods where theNET is not busy since contention is unlikely in this situation.

Channel sounding for Outbound messages is accomplished through a Requestfor Poll/Poll cycle where handshaking messages with short time outperiods must be successfully communicated before longer messagetransmissions may be attempted.

As discussed above with regard to FIG. 1, a premises LAN consists ofseveral base stations 15 located throughout an environment requiringwireless communications, e.g., a building or other facility, or a campuscomprised of several buildings. The base stations 15 are placed toprovide coverage of intended usage areas for the roaming portable ormobile computing devices 20. Coverage areas must overlap to eliminatedead spots between coverage areas.

The base stations 15 may be interconnected via industry standard wiredLANs, such as IEEE 802.3 Ethernet, or IEEE 802.5 Token Ring. Basestations may be added to an existing LAN without the need to installadditional LAN cable. Alternatively, it may be desirable to install basestations on dedicated LAN segments to maximize performance of both theradio network and other collocated computer devices.

Base stations within the premises LAN provide Control Point functionsfor individual NETs. NETs employ different hopping sequences to minimizepotential interference between NETs. Regulatory restrictions generallypreclude synchronization of multiple NETs to a single master clock,requiring that individual NETs operate independently from one another.The lack of the ability to coordinate timing or frequency usage betweenNETs introduces the potential for collisions between independent NETswith overlapping coverage areas.

FIGS. 9a and 9b illustrate conceptually how multiple NETs may beemployed in an idealized "cellular" type installation. Each hexagon 901and 903 in FIG. 9a represents the primary coverage area of a given NET.Coverage areas are modeled as circles 905 based upon some reliabilitycriterion, for example a 5% mean fragment retry rate (on average 95% offragments are successfully communicated on the first attempt). Typicalcoverage areas are determined by physical attributes of the area inwhich the NET operates. As is illustrated in FIG. 9b for the hexagon(NET) 903 of FIG. 9a, an actual coverage area 907 meeting thereliability criterion is likely to be irregular. This may require basestations to be offset significantly from the hexagonal grid.

FIG. 10 illustrates a coverage contour overlap for the multiple NETs inthe premises LAN of FIG. 1. Darken shaded areas 1001 indicate areaswhere base station coverage overlaps. Because the coverage distance of aradio system on an instantaneous basis greatly exceeds the coverage thatcan be provided on average to sustain a given quality of service, theoverlap at any instant may be significantly greater than the coveragecontours indicate.

FIG. 11 illustrates hopping sequence reuse in a multiple NETconfiguration. Hopping sequence re-use may be necessary if there arephysical constraints on the number of hopping sequences that can besupported. For example, devices may have limited memory available forhopping sequence storage. Use of a smaller set of sequences alsosimplifies the task of determining sets of sequences that haveacceptable cross correlation properties. In FIG. 12, 7 hopping sequences1 through 7 are used throughout the coverage area. Other NETs may reusethe same hopping sequence at some distance removed. While 7 NETs areillustrated, larger numbers, such as 9 or 15 may provide a bettercompromise between minimizing the number of hopping sequences used, andreuse distance between NETs using the same sequence. Reuse requirescoordination of hopping sequence assignment--either the system installercan coordinate the installation, or the system may include automatedmanagement features to assign hopping sequences to individual NETs.

Since NETs are not synchronized, different NETs that use the samehopping sequence are likely to interfere during periods where oscillatordrift causes them to be temporarily synchronized. At other times, theymay only interfere due to imperfect channelization. For example, for aworst case 100 ppm frequency error between two NETs using the same 79frequency sequence at one Access Interval per hop and 50 hops persecond, NETs will partially or fully overlap for a duration of 10minutes every 4.3 hours. Typically the frequency error will be 25% to50% of the worst case, leading to longer overlap periods occurring lessfrequently.

NETs using the same hopping sequence must be physically isolated fromone another to reduce interference to an acceptable level. Extensivehopping sequence reuse generally requires site engineering andoptimization of base station placement. Using more hopping sequencesreduces the need for critical system engineering during installation.Fifteen hopping sequences is a preferred number for hopping sequencereuse, allowing simplified installation and minimal coordination.

NETs that use different hopping sequences will also temporarilysynchronize in timing relationships that cause mutual co-channelinterference on common channel frequencies. Since the number of channelsthat must be used in a sequence is a significant fraction of the totalnumber of channels available, all sequences will share some number offrequencies in common. When sequences are time aligned so that a commonfrequency is used simultaneously, interference can occur. Optimizationof sets of sequences for low cross correlation is necessary to preventvarious time alignments of sequences from having more than one or twofrequencies in common.

Optimization of hopping sequences for multiple NETs must also includeanalysis of imperfect channelization. The performance characteristics ofthe RF modems may not, for economic or power consumption reasons,provide sufficient transmitter spectral containment, receiver dynamicrange, or receiver selectivity to guarantee that devices operating ondifferent frequencies in proximity to one another will not interfere. Inselecting hopping sequences for desirable cross correlation properties,adjacent and alternate adjacent channel interference must be considered.Protocol retry mechanisms for fragments lost to adjacent channelinterference or limited dynamic range may be randomized to preventcontinued disruption of communications in the affected NET.

Often in campus environments where systems must provide coverage inseveral buildings, the cost of wiring LAN cable between base stations isprohibitive. To establish connectivity between base stations in anpremises LAN, it may be necessary to provide wireless links betweengroups of base stations connected to separate LAN segments. FIG. 12illustrates a wireless link 1201 connecting groups of base stations 1203and 1205. The base stations 1203 and 1205 are connected on separate LANsegments 1207 and 1209.

In one embodiment, the base stations 1203 and 1205 may be configured ina wireless point to point mode, wherein one base station serves as acontrol point device while the others operate in a slaved mode dedicatedto point to point data transfer. Slave base stations are configured tooperate as portable/mobile devices, and forward communications to masterbases by sending Request for Polls during reservation opportunities orImplicit Idle Sense periods. Because of the potential high traffic ofpoint to point links, separate NETs may be allocated for this purpose,with a master communicating with one or more slave units. Master unitsmay also communicate with other portable/mobile devices. The COSTweighing (discussed below) in a slave's HELLO transmission is preferablyset to a high value, to force portable/mobile devices which can connectto another NET to do so.

In another embodiment, it may also be desirable to support wireless basestations. Wireless base stations serve as control points, but are notconnected to the infrastructure through a LAN cable. As is illustratedin FIG. 13, a wireless base station 1301 participates in the premisesLAN through a wireless link 1303 to a base station 1305 that isconnected to a LAN 1307.

Wireless base stations operate as slave devices to master base stationswhich are connected to the wired infrastructure. The wired and wirelessbase stations share the same hopping sequence, and are synchronized as acommon NET. Because they are not connected to the Infrastructure,wireless base stations must be used as store and forward devices. Eachtransmission to a wireless base must be retransmitted to the intendeddestination device, doubling the number of transmissions occurring inthe NET. Wireless base stations are preferably used for supplementingcoverage area of the premises LAN. For example, a wireless base stationmight provide spot coverage of isolated "dead spots" where data trafficis limited or where providing a wired LAN connection is difficult.Wireless base stations may also serve as emergency spares to providecoverage in the event of a failure of a primary base station. In thisrole, the wireless base station may be either permanently installed inselected locations, or stored in a maintenance area and quicklypositioned and connected to AC or battery power to providecommunications while repairs are made to the primary wired base station.Moreover, permanently installed wireless base stations might also beused for redundancy, i.e., to monitor an associated base station and totake over when a breakdown is detected.

The preferred wireless base station embodiment uses interleaved accessintervals. The parent wired base station and secondary wireless basestation coordinate Access Intervals, the wired base station deferringevery third or sixth access interval to the wireless base. Since thewired base station transmits priority SYNC messages every third AccessInterval, the wireless base station may routinely be allocated one ofthe two intervening Access Intervals for priority SYNC communicationswith devices that are attached to it. Communication between the wiredand wireless base stations may occur during Access Intervals initiatedby either base station. Wireless base stations may also communicate withdevices during an Access Interval using Implicit or Explicit Idle Sense.

This embodiment provides predictable access for devices attached to thewireless NET, and allows the same power management algorithms to be usedregardless of whether the base station is wired or wireless. Thewireless base station may transmit its own priority SYNC and HELLOmessages. Also, devices seeking communications with the wireless basestation will automatically be synchronized with the wired base as well,allowing immediate improved access to the network if their mobility hasput them within range of the wired base.

Because of the constraint of sharing bandwidth with a wired basestation, connectivity of wireless base stations is normally limited toone per wired base station. However, in cases where system loading ispredictably and consistently light, multiple wireless base stationscould share a single wired base, e.g., each transmitting in turn in theAccess Intervals between the Wired Base Priority SYNC Access Intervals.

Wireless base stations are capable of supporting scheduled traffic.However, since each transmission to a wireless base station must beforwarded, scheduled transmissions through wireless base stations usetwice the bandwidth as those through wired base stations. In otherwords, twice the number of Time Division Multiple Access slots must beallocated. To avoid introducing excessive delay, communications must beforwarded during the same Access Interval that they are received, orshorter Access Intervals must be used. Scheduled traffic slotassignments must be common to all wireless bases operating within asingle NET.

Wireless base stations require reliable communication with their wiredcounterparts. This dictates smaller coverage contours for wireless basestations. If a wired base station provides 80,000 square feet ofcoverage area, a wireless base can be predicted to provide only anadditional forty percent coverage improvement, due to overlap with thewired base station. Frequently, base stations are mounted at ceilinglevel, providing a relatively clearer transmission path between basestations than exists between bases and portable/mobile devices locatedin more obstructed areas near the floor. With careful site engineeringand installation, a wireless base station can provide somewhat betterthan the forty percent predicted improvement, but still less than thecoverage of an additional wired base.

As discussed above, HELLO messages are used to communicate NET andpremises LAN status messages. They facilitate load leveling and roamingwithin the premises LAN and allow sequence maintenance to improvesecurity and performance within the NET. HELLO messages occurperiodically in Access Intervals that contain priority SYNC messages.HELLOs are sent periodically relative to the sequence length, forinstance, every 90 Access Intervals. HELLOs, like SYNC information, areoptionally encrypted to provide greater security.

Each HELLO message includes a field for COST. COST is a measure of thebase station to handle additional traffic. A device determining which oftwo or more base stations having adequate signal strength to registerwhich will select the base with the lowest COST factor.

The base computes COST on the basis of how many devices are attached tothe NET, the degree of bandwidth utilization, whether the base is wiredor wireless, the number of frequencies experiencing consistentinterference within the sequence, and the quality of the connection thebase has within the premises LAN.

FIG. 14 illustrates the concept of base stations communicatingneighboring base station information through HELLO messages tofacilitate roaming of portable/mobile devices. In a premises LAN, basestations 1401, 1403 and 1405 communicate SYNC information amongstthemselves via wired backbone (LAN) 1407. In addition, a wireless basestation 1409 (discussed above) similarly communicates with the basestations 1401, 1403 and 1405 via a wireless link 1411. A portable/mobiledevice 1413 is initially registered with base station 1401, which actsas a control point for the portable/mobile device 1413. HELLO messagestransmitted by base station 1401 to portable/mobile device 1413 containfields for neighboring base stations 1403, 1405 and 1409. These fieldsmay indicate, for example, addresses of the neighboring bases, theirCOST, the hopping sequences, hopping sequence indices, number of AccessIntervals per hop, and NET clock. The portable/mobile device 1413detects the HELLOs transmitted from base station 1401 and uses theinformation for coarse synchronization with the other base stations1403, 1405 and 1409. This permits the portable/mobile device to roambetween base station coverage areas (i.e., between different NETs)without going through a full acquisition phase. Roaming ofportable/mobile devices is discussed in more detail below.

Simply put, communication of neighbors' information permits each basestation to advise its associated portable/mobile devices (i.e., thosehaving common communication parameters) on how to capture HELLO messagesfrom neighboring base stations having different communicationparameters. Such communication parameters may include, for example,hopping sequences, spreading codes, or channel frequencies.

For example, neighbors' information transmission is appropriate in anycase where the system uses more than a single channel. For instance, ina direct sequence architecture, a single spreading code is often used.Capacity can be added to such a network by employing different spreadingcodes at each base station. The neighbors' information included in theHELLO message from a given base station would include the spreadingsequences of base stations providing coverage in adjacent coverageareas. Likewise, in a multiple frequency channelized system, HELLOmessages would include the channel frequencies of adjacent basestations.

In addition to facilitating roaming, communication of neighbors'information may also facilitate the initial selection of a base stationby a portable/mobile device attaching to the premises LAN for the firsttime.

Base station HELLO messages may also facilitate adaptive base stationtransmitter power control. For example, each base station HELLOtransmission could specify the transmitter power level being used by thebase station. If a given attached portable/mobile device notes that thecurrent base station transmitter power level is unnecessarily high(creating the possibility of interference with other base stations), theportable/mobile unit could send a message to the base station indicatingas such, and the base station could adjust the transmitter power levelaccordingly.

HELLO messages also enable communication of information indicating toall devices that certain changes in the NET are required. For example,the NET may switch hopping sequences periodically to improve security,or to avoid interference sources that consistently interfere with one ortwo frequencies within a given sequence. Interference may result fromoutside sources, or from other NETs. Changes to the NET are communicatedover the course of several HELLO messages (with a countdown) before thechange occurs, so that all devices are likely to be aware of changes andsynchronize at the instant of change.

In addition, if encryption is used, the encryption key may beperiodically changed in HELLOs. Like hopping sequence changes, KEYchanges are sent over several HELLOs, and are encrypted using theexisting key until the change goes into effect.

As mentioned above, roaming portable and mobile computing devicesoperating in the premises LAN will routinely move between base stationcoverage areas. At the maximum device velocity and expected coveragearea per base station, a mobile device may be expected to cross a NETcoverage contour in several seconds. Because of the use of multiple,non-synchronized frequency hopping NETs, it is more difficult to providefor simple hand-off between base stations than it would be in a systemthat used cellular techniques with a single frequency per cell. Thepremises LAN makes special provisions for roaming by transmitting coarsefrequency hopping synchronization information in HELLO messages.

The premises LAN uses a spanning tree algorithm to maintain currentinformation regarding the general location of mobile devices within thenetwork. When a device changes registration from one NET Control Pointto another, routing information is updated throughout theinfrastructure. Wired base stations may broadcast spanning tree updatesto attached wireless base stations.

In the premises LAN, roaming portable and mobile devices initiallyselect and register with a Base Station Control Point on the basis oflink quality, i.e., signal quality, signal strength and COST informationtransmitted within HELLO messages. A device will remain attached to aparticular base station until the link quality degrades below anacceptable level, then it will attempt to determine if an alternativeNET is available. Different device operating scenarios dictate differentroaming strategies, discussed below.

An idle device monitors SYNC and HELLO messages from the Control Pointdevice to maintain NET connectivity. Type 2 devices do not employ powermanagement, and always maintain their receivers in an active state. Theymonitor all SYNC messages. Type 1 and Type 3 devices typically employpower management, operating in standby or sleep modes of operation formany Access Intervals before activating their receivers for monitoringSYNC and HELLO messages. Control Points are guaranteed to send PrioritySYNC frames every third Access Interval. HELLOs occur every 30thPriority SYNC frame. Power managed devices employ sleep algorithmssynchronized to wake for the minimum period necessary to guaranteereceipt of priority SYNC, HELLO, and Pending Message transmissionsbefore resuming SLEEP.

Type 2 devices are typically operated from high capacity vehicular powersystems, which eliminates the need for power management. These-devicesmay travel at velocities near the maximum system design specification,dictating more frequent roaming. Type 2 devices will initiate a searchfor an alternative NET if SYNC messages are consistently received atsignal strengths below a Roaming Threshold or if reception errors areconsistently detected. Because of the effects of frequency selectivefading, signal strength information is averaged over the course ofseveral hops within the hopping sequence.

If roaming is indicated, the device initiates a Roaming Algorithm, usingNeighbors' information from the most recent HELLO to attemptsynchronization with another candidate NET. If SYNC is not detectedwithin 6 hops, another candidate from the Neighbors list will beselected, and the process repeated. Once SYNC is attained on analternative NET, the device will monitor signal strength and data errorsfor several hops to determine link quality. If link quality isacceptable, the device will continue monitoring until a HELLO isreceived. If COST is acceptable, it will then register with the new NET.The Control Point device will update the Spanning Tree over the wiredbackbone (or by RF if a wireless base). If link quality or COST isunacceptable, another candidate from the Neighbors list is selected andthe process repeated. This continues until an acceptable connection isestablished. If a connection cannot be established, the device mustreturn to the original NET or employ the initial acquisition algorithm.

Type 2 devices also have the option of monitoring other NETs beforedegradation of their NET connection. They may do so by monitoring theirown NET for the SYNC and pending message list transmissions, thenscanning other candidate NETs during the Sessions period of their NET.Other type devices may do so less frequently.

Type 1 and Type 3 devices may sleep extensively when idle, preferablyactivating every nine Access Intervals to resynchronize and checkpending messages. Successful reception of at least one SYNC during threemonitoring periods is necessary to maintain fine synchronization to theNET clock. Failure to receive two of three SYNC frames, or receipt oftwo or three SYNC messages with poor signal strength are possibleindications of the need to further test link quality by remaining activefor several consecutive SYNC transmissions. If signal strength or dataerrors over several hops indicates that link quality is poor, or if areceived HELLO message indicates high COST, the roaming algorithm isinitiated, and alternative NETs are evaluated, as in the case of Type 2devices.

Some battery powered devices may sleep for periods of time more thannine Access Intervals. For example, devices with extremely limitedbattery capacity may sleep between HELLOs, or several HELLO periods,after which they must remain active for several consecutive AccessIntervals to regain fine synchronization and assess whether to initiateroaming.

A Type 1, Type 2, or Type 3 device that has inbound message requirementsimmediately activates its receiver and waits for a SYNC and subsequentReservation Opportunities. A device that does not detect SYNC messagesover the course of six Access Intervals immediately initiates theRoaming Algorithm.

Outbound messages for devices that have changed coverage areas, butwhich have not yet registered with a new Control Point device, areproblematic. For example, in the premises LAN, messages will beforwarded to the Base Station that the device had previously beenattached to. The base station may attempt to poll the device during oneor more Access Intervals, then transmit the unit address in the pendingmessage list periodically for several seconds before disregarding it.Once the unit attaches to a base, the message must be transferred fromthe previous base station for delivery to the unit. All of theseactivities require transmission bandwidth on either the backbone or RFmedia, waste processing resources within the premise LAN, and result indelayed delivery.

As this premises LAN embodiment is designed, the network has no means ofdistinguishing messages it cannot deliver due to roaming from messagesthat should be retried due to signal propagation characteristics,interference, or sleeping devices. For this reason, the roamingalgorithm may be designed to allow devices to quickly detect that theyhave lost connectivity within their current NET, and re-attach to a morefavorably located base station.

Some improvement in delivering pending messages to roaming terminals canbe obtained by routinely propagating pending message lists over thewired backbone. When a device attaches to a base station, that base isable to immediately ascertain that the device has a pending message, andinitiate forwarding of the message for delivery to the device.

In the preferred frequency hopping embodiment of the present invention,the hopping sequence consists of 3m±1 frequencies, where m is aninteger. 79 frequencies are preferred. This embodiment will supporthopping rates of 100, 50 hops per second at 1 Access Interval per dwell,25 hops per second at 2 frames per dwell, and 12.5 hops per second at 4frames per dwell. Other rates can be supported for other Access IntervalDurations. For example, if the Access Interval is optimized to 25 ms,hop rates of 80, 40, 20, and 10 hops per second would be supported.

All devices within the NET may have one or more hopping tables thatcontain potential hopping sequences that may be used. Up to 64 sequencesmay be stored in each device. Each sequence has an identifier, and eachfrequency in each sequence has an index. The sequence identifier andindex are communicated in the SYNC transmission.

All SYNC transmissions may be block encrypted to prevent unauthorizeddevices from readily acquiring hopping synchronization information. Tofacilitate encryption, the encryption key may initially be factory setto a universal value in all devices. Users would then have the option ofchanging this key, by providing a new key to each device in the system.This may be accomplished through keyboard entry or other secure means.Keys may also be changed through the NET.

To facilitate hopping management, a hopping control portion of aprotocol controller will download a hopping table to a radio modem, andwill signal the radio modem when to hop. This approach consolidatestiming functions in the protocol controller, while not requiring thecontroller to be concerned with conveying frequency selection data tothe modem each hop.

The NET may switch hopping sequences periodically to improve security,or to avoid interference sources that consistently interfere with one ortwo frequencies within a given sequence. As mentioned above, changes tothe NET are communicated over the course of several HELLO messagesbefore the change occurs so that all devices are likely to be aware ofchanges.

Initial synchronization requires devices to ascertain the hoppingsequence, the hop rate, and the specific frequency from the hoppingsequence currently in use. Synchronization information is contained intwo types of routine messages. The SYNC field at the beginning of anAccess Interval contains synchronization information including thehopping sequence, the index of the current frequency within thesequence, the number of Access Intervals per hop, and the length of theAccess Interval. It also contains a timing character that communicatesthe NET master clock to all listening devices. Termination messages inthe Sessions period, ACK and CLEAR, contain the same information, but donot contain the timing character.

The simplest method for attaining synchronization is to Camp--select aquiet frequency that is likely to be within a sequence in use--andlisten for valid synchronization information. If a SYNC message isdetected, the listening device immediately has both coarse and finesynchronization, and can begin the registration process.

If SYNC is not detected, but a termination message is, then the devicehas acquired coarse synchronization. The particulars of the hoppingsequence are known, but the boundaries of the dwells are not. To acquirefine synchronization, it begins hopping at the indicated hopping rate,listening for SYNC. If SYNC is not detected after a reasonable number ofhops, preferably 12 or 15, the device reverts to camping.

The worst case scenario for synchronization is to synchronize to asingle NET that is idle. Given a 79 frequency hopping sequence, oneAccess Interval per hop, and SYNC transmissions every third AccessInterval if the NET is idle, it may take nine cycle times to guaranteethat a SYNC transmission will be detected with 99.5% probability. At 50hops per second, synchronization could require as long as 14 seconds. At100 hops per second, 7 seconds is required.

At 2 Access Intervals per hop, a SYNC transmission is guaranteed tooccur every frequency over 2 cycles of the hopping sequence. Six cyclesare required for 99.5% probability of acquisition, corresponding to 19seconds at 25 hops per second.

At 4 Access Intervals per hop, at least one SYNC is guaranteed to occureach hop. Three cycles of the hopping sequence are required for 99.5%acquisition probability. At 12.5 hops per second, this also requires 19seconds.

This illustrates the advantage of scalability. A device that uses anacquisition algorithm suitable for 2 or 4 Access Intervals per hop willalso acquire a NET that hops at 1 Access Interval per hop. The algorithmmay be as follows:

1. The device scans candidate frequencies until it finds one with noReceived Signal Strength Indicator indication.

2. The device remains on the frequency for 6.32 seconds 2 AccessInterval/hop @ 25 Hops/second×2, or 4 Access Interval/hop @ 12.5hops/second×1, or until it detects a SYNC message or a valid terminationmessage.

3. If SYNC is detected, the device synchronizes its internal clock tothe SYNC, and begins hopping with the NET for the next 11 hops. It mayattempt registration after detecting valid SYNC and any Reservationopportunity. If synchronization is not verified by detection of SYNCwithin the 11 hops, the acquisition algorithm is reinitialized.

4. If a message termination (either an ACK or CLEAR) is detected, thedevice immediately hops to the next frequency in the sequence and waitsfor the SYNC. It is coarsely synchronized to the NET but has a timingoffset from the NET clock.

When the next SYNC is received, the device synchronizes its clock to theNET clock and initiates registration. If SYNC is not received within adwell time, the device hops to the next frequency in sequence. Thiscontinues until SYNC is attained, or until 15 hops have passed withoutreceiving SYNC, after which the acquisition sequence is restarted.

5. If coarse acquisition is not obtained within 6.3 seconds, the deviceselects another frequency and repeats the process beginning with step 2.

Camping provides a worst case acquisition performance that isperceptibly slow to the human user of a portable device. The preferredapproach has the receiver scan all potential frequencies in ascendingorder, at 125 μsec increments. When the highest frequency is reached,the search begins again at the lowest frequency. The 125 μs samplingrate is much faster than the 250 μsec channel switching timespecification of the RF modem. This is possible because the overallswitching time specification applies to worst case frequency switchingintervals, i.e., from the highest to the lowest operating frequency. Byswitching a single channel at a time, switching may be maintained overfrequency intervals very near a synthesizer phase detectors' phase lockrange, allowing nearly instantaneous frequency switching. The changefrom highest to lowest frequency at the end of the scan requires thestandard 250 μsec.

The 125 μsec monitoring interval allows 85 μs to ascertain if receiveclock has been detected prior to switching to the next frequency. Themonitoring interval should be selected to be non-periodic with respectto the access interval. For example, the 125 μsec interval allows theentire hopping sequence to be scanned 2(n+1) times in a 20 ms accessinterval.

If clock is recovered at any frequency, the receiver remains onfrequency for a Reservation Opportunity and initiates channel accessthrough the procedure described above. The scanning approach is lessdeterministic in terms of acquisition probability than camping, but thesearch time required for 99.5% acquisition probability is about 80Access Intervals, or three times faster than that for camping.

A hybrid approach that scans only three or four consecutive frequenciesincorporates the deterministic aspects of camping with some of theimproved performance of the scanning algorithm. For scanning over asmall number of frequencies an up/down scan is preferred, i.e.,1,2,3,2,1,2,3 since all frequency changes can be accomplished at thefaster switching rate. The end frequencies are visited less often thanthose in the center. The number of frequencies used, e.g., 3 or 4, isselected so that all can be scanned during the preamble duration of aminimum length transmission.

All devices are required to have unique 48 bit global addresses. Local16 bit addresses will be assigned for reduced overhead incommunications. Local addresses will not be assigned to devices whoseglobal addresses are not on an authentication list maintained in eachbase station and routinely updated over the infrastructure.

Once a device has attained synchronization, it must register with thecontrol point to be connected with the NET. It initiates this by sendinga Request for Poll indicating a registration request, and including itsglobal address. The control point will register the device, and providea short. Network Address as an outbound message. The Control point willgenerate the short address if it is a single NET, or exchange the globaladdress for a short Network Address with a Network Address Server if theNET is part of a larger infrastructured network of a premises LAN.

Once a device is synchronized to a NET, it must periodically update itslocal clock to the NET clock communicated in the SYNC message. The SYNCmessage contains a character designated as the SYNC character thattransfers the NET clock synchronization. This may be the beginning orending FLAG in the SYNC message, or a specific character within themessage.

The maximum expected frequency error between NET and device local clocksis 100 parts per million. To maintain a 50 μs maximum clock error, thelocal device clock must be re-synchronized at 500 ms intervals. At 20 msper access interval, a non-sleeping device has up to 26 SYNCopportunities within that period in which to re-synchronize and maintainrequired accuracy.

As mentioned above, it is desirable that battery powered devices havethe capability to sleep, or power off, for extended periods of time toconserve power. The term sleeping terminal in this instance may refer toa device that powers down its radio communication hardware to save powerwhile maintaining other functions in an operational state, or a devicethat power manages those functions as well. In the power managed state,the device must maintain its hop clock so that full acquisition is notrequired every time power management is invoked.

Devices that must sleep to manage their power consumption use PrioritySYNC Messages to maintain synchronization. Priority SYNC Messages occurevery three Access Intervals. In times of low NET activity, non-prioritySYNC messages are omitted. By coordinating power management withPriority SYNC Messages, power managed devices can be guaranteed to wakeup for Access Intervals where SYNCs will be present, even if the NETactivity is low during the sleep period.

A sleeping device with no transmission requirements may sleep for eight20 ms access intervals, and wake only for the SYNC and Reservation Pollat the beginning of the ninth Access Interval to monitor pendingmessages before returning to the sleep state, for a duty cycle of lessthan 5%. This provides three opportunities to synchronize to the NETclock within a 540 ms window. A flow chart depicting the a devicesleeping for several access intervals is shown in FIG. 17.

Devices may also sleep for longer periods of time, at the risk of losingfine synchronization. They may compensate by advancing their localclocks to account for the maximum timing uncertainty. For example, aterminal could sleep for 5 seconds without re-synchronizing by waking up500 microseconds before it expects an Access Interval to begin, andsuccessfully receive SYNC messages. This technique is valid for extendedperiods of time, up to the point where the maximum timing errorapproaches 50% of an Access Interval. A flow chart depicting the adevice sleeping for several seconds is shown in FIG. 18.

A power managed device that requires communication during a sleep periodmay immediately wake and attempt access to the NET at the next availableReservation Opportunity.

A device requiring communications may be able to register with one ofseveral NETs operating in its vicinity, with transmissions occurring onmany frequencies simultaneously. A good strategy is to synchronize to aNET that provides an acceptable communication link, then monitor HELLOmessages to determine other candidate NETs before attaching to aparticular NET by registering with the control point device.

As described above, a spontaneous wireless local area network orspontaneous LAN is one that is established for a limited time for aspecific purpose, and which does not use the premises LAN to facilitatecommunications between devices or provide access to outside resources.Use of spontaneous LAN allows portable devices to share information,files, data, etc., in environments where communication via the premisesLAN is not economically justifiable or physically possible. Aspontaneous LAN capability also allows portable/mobile devices to havean equally portable network. Peripheral and vehicular LANs are examplesof such spontaneous LANs.

Requirements for spontaneous LAN differ from an infrastructured premisesLAN in several significant areas. The number of devices in a spontaneousLAN is likely to be smaller than the number that a single NET in apremises LAN must be capable of supporting. In addition, coverage areasfor spontaneous LANs are typically smaller than coverage areas for abase station participating in the premises LAN. In a spontaneous LAN,communication often takes place over relatively short distances, wheredevices are within line of sight of each other.

In an premises LAN, the majority of communications are likely to involveaccessing communication network resources. For example,. portabledevices with limited processing capabilities, memory, and power suppliesare able to access large databases or powerful computing enginesconnected to the AC power grid. Base stations within the premises LANare well suited to the role of Control Points for managingsynchronization and media access within each NET.

In a spontaneous LAN, however, communications are limited to exchangeswith spontaneous NET constituents. Additionally, NET constituents maypotentially leave at any time, making it difficult to assign controlpoint responsibilities to a single device. A shared mechanism forsynchronization and media access is preferable in most cases.

In a spontaneous LAN, battery power limitations may preclude assignmentof a single device as a control point. The routine transmission of SYNCand access control messages places a significant power drain on aportable, battery powered device. Also, the control point architecturedictates that transmissions intended for devices other than the controlpoint be stored and forwarded to the destination device, furtherincreasing battery drain, and reducing system throughput.

Moreover, the use of scheduled transmission in a premises LAN is likelyto differ from use in a spontaneous LAN. For example, unlike thepremises LAN, in the spontaneous LAN, applications such as massaging andtwo way voice communications may only occasionally be used, whereasvideo transmission and telemetry exchange may be prevalent.

To promote compatibility and integration with the premises LAN,operational differences required by multiple participating devicesshould be minimized. For example, selecting relatively close frequencybands for each LAN aids in the design of a multiple LAN transceiver,reducing circuitry, cost, power, weight and size while increasingreliability, similarly, selecting communication protocols so that thespontaneous LAN protocol constitutes a subset or superset of premisesLAN may enable a given device to more effectively communication in bothLANs, while minimizing both the overall protocol complexity andpotentially limited memory and processing power.

Use of frequency hopping is desirable in premises LAN because of itsability to mitigate the effects of interference and frequency selectivefading. In the case of the latter, frequency hopping allows systems tobe installed with less fade margin than single frequency systems withotherwise identical radio modem characteristics, providing improvedcoverage.

The potentially smaller coverage area requirement of spontaneous LANS,however, allows single frequency operation to be considered for someapplications, e.g., such as a peripheral LAN. Regulatory structures arein place in some countries to allow single frequency operation in thesame bands as frequency hopping systems, providing that single frequencydevices operate at reduced power levels. The lower transmit power ofsingle frequency operation and elimination of periodic channel switchingare desirable methods of reducing battery drain. The choice of singlefrequency or frequency hopped operation is dictated by the coveragerequirements of the network, and may be left as an option to deviceusers.

As noted earlier, the basic Access Interval structure is suited tosingle frequency operation as well as to frequency hopping. SYNCmessages in a single frequency system substitute a single frequencyindication in the hopping sequence identifier field.

A spontaneous LAN comes into existence when two or more devicesestablish communications, and ceases when its population falls to lessthan two. Before a spontaneous LAN can be established, at least twodevices agree upon a set of operating parameters for the network. Suchagreement may be pre-programmed else exchanged and acknowledged prior toestablishing the spontaneous LAN. Once the spontaneous LAN isestablished, other devices coming into the network must be able toobtain the operating parameters and acquire access.

More specifically, to establish a spontaneous LAN, a computing devicemust first identify at least one other network device with whichspontaneous LAN communication is desired. To identify another networkdevice, the computing device may play an active or passive role. In anactive role, the computing device periodically broadcasts a request toform spontaneous LAN with either a specific network device or, morelikely, with a specific type of network device. If a network devicefitting the description of the request happens to be in range or happensinto range and is available, it responds to the periodic requests tobind with the computing device, establishing the spontaneous LAN.Alternately, the network device may take a passive role in establishingthe spontaneous LAN. In a passive role, the computing device merelylistens for a request to form a spontaneous LAN transmitted by theappropriate network device. Once such a network device comes into range,the computing device responds to bind with the network device,establishing the spontaneous LAN.

The choice of whether a device should take a passive or active role is amatter of design choice. For example, in one embodiment where peripheraldevices have access to AC power, the roaming computer terminals take apassive role, while the peripheral devices take a more active role.Similarly, in another embodiment where a vehicle terminal has access toa relatively larger battery source, an active role is taken whenattempting to form a spontaneous LAN, i.e., a vehicular LAN, with ahand-held computing device.

Binding, a process carried out pursuant to a binding protocol stored ineach network device, may be a very simple process such as might existwhen creating a spontaneous LANs that operates on a single frequencychannel. Under such a scenario, a simple acknowledge handshake betweenthe computing terminal and the other network device may be sufficient toestablish a spontaneous LAN pursuant to commonly stored, pre-programmedoperating parameters. However, more complex binding schemes may also beimplemented so as to support correspondingly more complex spontaneousLANs as proves necessary. An example of a more complex binding scheme isdescribed below.

It is desirable in some large spontaneous LANs for one device to bedesignated as a fully functional control point, providing identical NEToperation to a single NET in the premises LAN. Providing that alldevices share a hopping table and encryption key, the designated devicewould initiate control point activities, and other devices wouldsynchronize to the designated unit. A device with greater batterycapacity, or one that can be temporarily connected to AC power is bestsuited to the dedicated control point function. This architecture isapplicable to Client-Server applications (where the server assumes thecontrol point function), or to other applications where a single deviceis the predominant source or destination of communications. A portabledevice used as a dedicated control point is required to have additionalprogramming and memory capacity to manage reservation based mediaaccess, pending message lists, and scheduled service slot allocations.

In embodiments where communication requirements of a spontaneous LAN arelargely peer to peer, there may be no overwhelming candidate for adedicated Control Point. Thus, in such cases, the Control Point functionis either distributed among some or all the devices within thespontaneous LAN. In such scenarios, the interleaved Access Intervalapproach used for wireless base stations is employed. Initially, controlpoint responsibilities are determined during the binding process. Usersmay designate or redesignate a Control Point device when severalcandidates are available.

For spontaneous LANs, access intervals may be simplified to reduce powerconsumption, program storage and processing power requirements forportable devices used as control points. Control Point devices transmitSYNC, pending message lists, and Time Division Multiple Access slotreservations normally, but only use the single slot reservation Poll(Idle Sense Multiple Access). The reservation poll contains a fieldindicating reduced control point functionality. This places otherdevices in a point-to-point communication mode, using the Implicit IdleSense Algorithm. The probability factor p communicated in thereservation poll is used for the Implicit Idle Sense algorithm. Controlpoint devices may use the deferred SYNC mechanism for light systemloading, transmitting Priority SYNC every third Access Interval tofurther decrease their transmission requirements. Control point devicesmust monitor the reservation slot for messages addressed to them, butmay sleep afterwards.

Request for Polls initiated under Implicit Idle Sense use point-to-pointaddressing, indicating the address of the destination device directly,rather than the control point device. This eliminates the need for theControl Point device to store and forward transmissions within thespontaneous LAN. The device detecting its address in a Request for Pollbegins a session, after employing the Implicit Idle Sense algorithm, byPolling the source address identified in the Request for Poll. Theterminating ACK and CLEAR messages contain an Explicit Idle Senseprobability factor equal to that in the original reservation poll.

To allow for power managed devices, the Control Point device maintains apending message list. Devices that have been unable to establishcommunication with a sleeping device initiate a session with the ControlPoint device to register the pending message. Upon becoming active, thesleeping device will initiate a Poll to the device originating thepending message. The Control Point device will eliminate the pendingmessage indication by aging, or by receipt of communication from thedestination device clearing the pending message. Control point devicesare not required to store pending messages, only addresses.

As mentioned above, HELLO messages are broadcast to indicate changes inNET parameters. HELLO messages may be omitted to simplify the ControlPoint function in spontaneous LANs.

Devices are assigned local addresses upon registration with the ControlPoint device. Devices may communicate an alias that identifies thedevice user to other users to the Control Point device where it isstored in an address table. The address table may be obtained by othernetwork constituents by querying the Control Point device. A peripheralLAN is a type of spontaneous LAN which serves as a short rangeinterconnect between a portable or mobile computing device (MCD) andperipheral devices.

Designers of portable products are constantly challenged with reducingsize, weight, and power consumption of these devices, while at the sametime increasing their functionality and improving user ergonomics.Functions that may be used infrequently, or which are too large to fitwithin the constraints of good ergonomic design may be provided inperipheral devices, including printers, measurement and data acquisitionunits, optical scanners, etc. When cabled or otherwise physicallyconnected to a portable product, these peripherals often encumber theuser, preventing freedom of movement or mobility. This becomes moreproblematic when use of more than one peripheral is required.

A second consideration for portable product design is communicationdocking. A communication dock is a device that holsters or houses aportable unit, and provides for communication interconnection for suchtasks as program downloading, data uploading, or communication withlarge printers, such as those used for printing full sized invoices invehicular applications. Communication docking of a portable unit mayalso involve power supply sharing and/or charging.

The requirement for communication docking capability forces newerportable product designs to be mechanically compatible with olderdocking schemes, or may require that new docks, or adapters, bedeveloped for each new generation of portable device. Product specificdocking approaches eliminate compatibility between devices manufacturedby different suppliers. This has hindered development of uniformstandards for Electronic Data Interchange between portable devices andfixed computing systems.

Physical connection between a portable device with a peripheral orcommunication dock also hinders user efficiency. Peripheral devices aregenerally attached with cable. If a peripheral is small enough to becarried or worn on a belt, the mobility of the user may be maintained.If a user must carry a hand-held portable device that is connected to abelt mounted peripheral the assembly cannot be set down while a taskthat requires movement to a location several feet away is undertakenunless the portable device and peripheral are disconnected. Likewise,connection to peripherals too large to be portable requires the user tofrequently connect and disconnect the device and the peripheral.

Use of wireless peripheral LAN interconnection greatly simplifies thetask of portable devices communicating with peripherals. In doing so,wireless connectivity allows improved ergonomics in portable productdesign, flexibility in interconnection to one or more peripherals,freedom of movement over a radius of operation, forward and backwardcompatibility between portable units and peripherals, and potentialcommunications among products manufactured by different vendors.

Constituents within a peripheral LAN generally number six or fewerdevices. One roaming computing device and one or two peripheralscomprise a typical configuration. Operating range is typically less thanfifty feet.

Because the computing devices generally control the operation ofperipheral devices, in a peripheral LAN a master/slave type protocol isappropriate. Moreover, roaming computing devices serving as master arewell suited to the role of Control Points for managing synchronizationand media access within each peripheral LAN. All peripheralcommunications are slaved to the master.

In a peripheral LAN, roaming mobile or portable computing devices andwireless peripherals may all operate from battery power. Operatingcycles between charging dictate use of power management techniques.

Although all participants in a peripheral LAN might also be configuredto directly participate in the premises LAN, the trade-offs in cost,power usage and added complexity often times weighs against suchconfiguration. Even so, participants within a peripheral LAN can beexpected to function in a hierarchical manner, through a multipleparticipating device, with the premises LAN. Thus, the use of a muchsimpler, lower-power transceiver and associated protocol may be used inthe peripheral LAN.

As previously described, a roaming computing device serving as a masterdevice may itself be simultaneously attempting to participate in othernetworks such as the premises or vehicular LANS. Considerable benefitsarise if the radio and processing hardware that supports operationwithin the wireless network can also support such operation. Forexample, a device that is capable of frequency hopping is inherentlysuited to single frequency operation. If it can adjust transmitter powerlevel and data rate to be compatible with the requirements of theperipherals LAN, it can function in both systems. The major benefits ofcommon transceiver hardware across LANs include smaller product size,improved ergonomics, and lower cost.

Specifically, in one embodiment, radio communication on the premisesLAN, as described herein, takes place using radio transceivers capableof performing frequency-hopping. To communicate on a peripheral LAN,such transceivers could also utilize frequency-hopping at a lower power.However, such transceivers are relatively expensive in comparison to alower power, narrow-band, single frequency transceivers. Because of thecost differential, it proves desirable to use the single frequencytransceivers for all peripheral devices which will not participate inthe premises LAN. Therefore, the more expensive, frequency-hoppingtransceivers which are fitted into roaming computing devices are furtherdesigned to stop hopping and lock into the frequency of the singlefrequency transceiver, allowing the establishment of peripheral LANS.

Instead of frequency hopping, the peripheral LAN may also usenarrow-band, single frequency communication, further simplifying theradio transceiver design for commonality. In another embodiment of theperipheral LAN transceivers, operation using one of a plurality ofsingle frequency channels is provided. Thus, to overcome interference onone channel, the transceiver might select from the remaining of theplurality an alternate, single operating frequency with lesser channelinterference. To accommodate the plurality of single frequency channels,the peripheral LAN transceivers may either communicate an upcomingfrequency change so that corresponding peripheral LAN participants canalso change frequency, or the transceivers may be configured to usefrequency synthesis techniques to determine which of the plurality acurrent transmission happens to be.

The Access Interval structure is also an appropriate choice forperipheral LAN operations. In one embodiment, to provide for simplicityand tighter integration, the Access Interval for the peripheral LAN is asubset of the Access Interval used in the premises LAN. HELLO messages,Implicit Idle Sense, Data Rate Switching, and scheduled services are notimplemented. Peripheral devices normally sleep, activate their receiversfor SYNC transmissions from the participating master device, and resumesleeping if no pending messages are indicated and they have no inboundtransmission requirements. Access Intervals occur at regular intervals,allowing for power management. Access Intervals may be skipped if themaster has other priority tasks to complete.

To initialize the peripheral LAN, a device desiring initialization, amaster device, selects a single operating frequency by scanning theavailable frequencies for one with no activity. A typical master devicemight be a roaming computing device desiring access to a localperipheral. Default values for other parameters, including AccessInterval duration, are contained within each participant's memory. Suchparameters may be preadjusted in each participant to yield specificperformance characteristics in the peripheral LAN.

Once a master device identifies a single frequency, slaves, which aregenerally peripherals, are brought into the peripheral LAN through aprocess called binding. Binding is initiated by the master device byinvoking a binding program contained therein. Slaves, such asperipherals, are generally programmed to enter a receptive state whenidle. Thus, in one embodiment, the master device accomplishes binding bytransmitting Access Intervals of known duration sequentially on a seriesof four frequencies spread throughout the available frequency range. Thespecific frequencies and Access Interval durations used are stored asparameters in all potential participating devices. A 250 KBPS transferrate is appropriate in some embodiments of the peripheral LAN,reflecting a balance between performance and complexity in peripheraldevices.

A slave, e.g., a peripheral, responds to the binding attempts by themaster device on a given frequency until the slave successfully receivesand establishes communication with the master device. If they do notestablish communication after four Access Intervals, the slave switchesto the next frequency for four Access Interval periods. Oncecommunication is established, the slave registers with the master andobtains the master device's selected operating frequency and relatedcommunication parameters. When all slave devices have been bound, themaster terminates the binding program and normal operation at theselected single frequency may begin.

Referring to FIG. 15, in a hierarchical network, peripheral LAN mastersuse a secondary access interval 1501 that is synchronized to the AccessInterval of a parent (premises) LAN control point. Peripheral LAN AccessIntervals occur less frequently than premises LAN Access Intervals,e.g., every other or every third Priority SYNC Access Interval.

During the premises LAN Access Interval, the peripheral LAN masterdevice monitors the premises LAN control point for SYNC 1503 reservationpoll 1505 and exchanges inbound and outbound message according to thenormal rules of the access protocol. The master switches to theperipheral LAN frequency, and transmits its own SYNC frame 1507 duringthe session period 1509 of its parent control point allowingcommunication with its peripherals. The peripheral LAN Access Intervalis generally shorter than the premises LAN Access Interval, so that itdoes not extend beyond the premises LAN Access Interval boundary. At theend of the peripheral LAN Access Interval 1501, the master switches tothe premises LAN frequency for the next SYNC 1503.

The secondary SYNC 1507 may only be transmitted if the peripheral LANmaster is not busy communicating through the premises LAN. If acommunication session is occurring, the master must defer SYNC,preventing communication with its peripherals during that AccessInterval. The master must also defer SYNC if the current frequency inthe LAN is prone to interference from the peripheral LAN frequency,i.e., they are the same frequency or adjacent frequencies. If twoconsecutive SYNCs are deferred, peripherals will activate theirreceivers continuously for a period of time, allowing the master totransmit during any Access Interval. This approach is also applicablewhen the master roams between frequency hopping NETS. Since NETs are notsynchronized to one another, the devices in the peripheral LAN adjustAccess Interval boundaries each time the master roams. If peripherals donot detect SYNC within a time-out period, they may duty cycle theirreception to conserve battery power.

Referring to FIG. 16, a Roaming Algorithm Flow Diagram illustrates how aroaming computing device will select a suitable base station. Roamingcomputing devices operating in the infrastructured network environmentformed by the base stations will routinely move between base stationcoverage areas. The roaming computing devices are able to disconnectfrom their current base station communication link and reconnect acommunication link to a different base station, as necessitated bydevice roaming.

Base stations transmit HELLO messages to devices in their coverage area.These HELLO messages communicate to roaming computing devices the costof connection through the base station, addresses of neighboring basestations, and the cost of connection through these neighboring basestations. This information allows roaming computing devices to determinethe lowest cost connection available and to connect to the base stationwith the lowest cost.

In addition, base station HELLO message may include communicationparameters of neighboring base stations, such as frequency hoppingsequences and indices, spread spectrum spreading codes, or FM carrierchannel frequencies. This information allows roaming computing devicesto roam and change base station connections without going through a fullacquisition phase of the new base station's parameters.

Roaming computing devices initially select and register with a basestation control point on the basis of link quality: signal strength andcost information transmitted within HELLO messages. A device will remainattached to a particular base station until the link quality degradesbelow an acceptable level; then it will attempt to determine if analternative base station connection is available. The device initiates aroaming algorithm, using neighbors information from the most recentHELLO message to attempt connection with another candidate base station.If connection fails, another candidate from the neighbors list will beselected, and the process repeated. Once connection is made with analternative base station, the device will monitor signal strength anddata errors to determine link quality. If link quality is acceptable,the device will continue monitoring until a HELLO message is received.If the cost is acceptable, it will register with the new base station,and the base station will update the spanning tree over theinfrastructure. If link quality or cost is unacceptable, anothercandidate from the neighbors list is selected and the process repeated.This continues until an acceptable connection is established. If onecannot be established, the device must return to the original basestation connection or employ the initial acquisition algorithm.

FIG. 28a illustrates an embodiment of the hierarchical communicationsystem according to the present invention where communication ismaintained in a warehouse environment. Specifically, a worker utilizes aroaming computing device, a computer terminal 3007, and a code reader3009 to collect data such as identifying numbers or codes on warehousedgoods, such as the box 3010. As the numbers and codes are collected,they are forwarded through the network to a host computer 3011 forstorage and cross-referencing. In addition, the host computer 3011 may,for example, forward cross-referenced information relating to thecollected numbers or codes back through the network for display on theterminal 3007 or for printing on a printer 3013. The host computer 3011can be configured as a file server to perform such functions. Similarly,the collected information may be printed from the computer terminal 3007directly on the printer 3013. Other exemplary communication pathwayssupported include message exchanges between the computer terminal 3007and other computer terminals (not shown) or the host computer 3011.

The host computer 3011 provides the terminal 3007 with remote databasestorage, access and processing. However, the terminal 3007 also providesfor local processing within its architecture to minimize the need toaccess the remote host computer 3011. For example, the terminal 3007 maystore a local database for local processing. Similarly, the terminal3007 may run a variety of application programs which never, occasionallyor often need access to the remote host computer 3011.

Many of the devices found in the illustrative network are batterypowered and therefore must conservatively utilize their radiotransceivers. For example, the hand-held computer terminal 3007 receivesits power from either an enclosed battery or a forklift battery (notshown) via a communication dock within the forklift 3014. Similarly, thecode reader 3009 operates on portable battery power as may the printer3013. The arrangement of the communication network, communicationprotocols used, and data rate and power level adjustments help tooptimize battery conservation without substantially degrading networkperformance.

In the illustrated embodiment shown in FIG. 28a, the hierarchicalcommunication system of the present invention consists of a premises LANcovering a building or group of buildings. The premises LAN in theillustrated embodiment includes a hard-wired backbone LAN 3019 and basestations 3015 and 3017. A host computer 3011 and any other non-mobilenetwork device located in the vicinity of the backbone LAN 3019 can bedirectly attached to the backbone LAN 3019. However, mobile devices andremotely located devices must maintain connectivity to the backbone LAN3019 through either a single base station such as the base station 3015,or through a multi-hop network of base stations such as is illustratedby the base stations 3015 and 3017. The base stations 3015 and 3017contain a relatively higher power transmitter, and provide coverage overthe entire warehouse floor. Although a single base station may besufficient, if the warehouse is too large or contains interferingphysical barriers, the multi-hop plurality of base stations 3017 may bedesirable. Otherwise, the backbone LAN 3019 must be extended to connectall of the base stations 3017 directly to provide sufficient radiocoverage. Through the premises LAN, relatively stable, longer rangewireless and hard-wired communication is maintained.

Because roaming computing devices, such as the hand- held computerterminal 3007, cannot be directly hard-wired to the backbone LAN 3019,they are fitted with RF transceivers. To guarantee that such a networkdevice can directly communicate on the premises LAN with at least one ofthe base stations 3015 and 3017, the fitted transceiver is selected toyield approximately the same transmission power as do the base stations3015 and 3017. However, not all roaming network devices require a directRF link to the base stations 3015 and 3017, and some may not require anylink at all. Instead, with such devices, communication exchange isgenerally localized to a small area and, as such, only requires the useof relatively lower power, short range transceivers. The devices whichparticipate in such localized, shorter range communication formspontaneous LANs.

For example, the desire by a roaming terminal to access peripheraldevices such as the printer 3013 and modem 3023, results in the roamingterminal establishing a peripheral LAN with the peripheral devices.Similarly, a peripheral LAN might be established when needed to maintainlocal communication between a code scanner 3009 and the terminal 3007.In an exemplary embodiment, the printer 3013 is located in a warehousedock with the sole assignment of printing out forms based on the codeinformation gathered from boxes delivered to the dock. In particular, assoon as the code reader gathers information, it relays the informationalong a peripheral LAN to the terminal 3007. Upon receipt, the terminal3007 communicates via the premises LAN to the host computer 3011 togather related information regarding a given box. Upon receipt of therelated information, the terminal 3007 determines that printing isdesired with the printer 3013 located at the dock. When the forklift3614 enters the vicinity of the dock, the terminal 3007 establishes aperipheral LAN with the printer 3013 which begins printing the collectedcode information.

To carry out the previous communication exchange, the printer 3013 andcode reader 3009 are fitted with a lower power peripheral LANtransceivers for short range communication. The computer terminal 3007transceiver is not only capable of peripheral LAN communication, but isalso capable of maintaining premises LAN communication. In an alternateexchange however, the code reader 3009 might be configured toparticipate on both LANs, so that the code reader 3009 participates inthe premises LAN to request associated code information from the hostcomputer 3011. In such a configuration, either the code reader 3009 orterminal 3007 could act as the control point of the peripheral LAN.Alternately, both could share the task.

With capability to participate in the peripheral LAN only, the codereader 3009, or any other peripheral LAN participant, might still gainaccess to the premises LAN indirectly through the terminal 3007 actingas a relaying device. For example, to reach the host computer 3011, thecode reader 3009 first transmits to the computer terminal 3007 via theperipheral LAN. Upon receipt, the computer terminal 3007 relays thetransmission to one of the base stations 3015 and 3017 for forwarding tothe host 3011. Communication from the host 3011 to the code reader 3009is accomplished via the same pathway.

It is also possible for any two devices with no access to the premisesLAN to communicate to each other. For example, the modem 3023 couldreceive data and directly transmit it for printing to the printer 3013via a peripheral LAN established between the two. Similarly, the codereader 3009 might choose to directly communicate code signals through aperipheral LAN to other network devices via the modem 3023.

In an alternate configuration, a peripheral LAN base station 3021 isprovided which may be directly connected to the backbone LAN 3019 (asshown), acting as a direct access point to the backbone LAN 3019, orindirectly connected via the base stations 3015 and 3017. The peripheralLAN base station 3021 is positioned in the vicinity of other peripheralLAN devices and thereafter becomes a control point participant. Thus,peripheral LAN communication flowing to or from the premises LAN avoidshigh power radio transmissions altogether. However, it can beappreciated that a stationary peripheral LAN base station may not alwaysbe an option when all of the peripheral LAN participants are mobile. Insuch cases, a high power transmission to reach the premises LAN may berequired.

FIG. 28b illustrates other features of the present invention in the useof spontaneous LANs in association with a vehicle which illustrate thecapability of automatically establishing a premises and a peripheral LANwhen moving in and out of range to perform services and report onservices rendered. In particular, like the forklift 3014 of FIG. 28a, adelivery truck 3033 provides a focal point for a spontaneous LANutilization. Within the truck 3033, a storage terminal 3031 is docked soas to draw power from the truck 3033's battery supply. Similarly, acomputer terminal 3007 may either be docked or ported. Because ofgreater battery access, the storage terminal 3031 need only beconfigured for multiple participation in the premises, peripheral andvehicular LANs and in a radio WAN, such as RAM Mobile Data, CDPD, MTEL,ARDIS, etc. The storage terminal 3031, although also capable of premisesand peripheral LAN participation, need only be configured for vehicularLAN participation.

Prior to making a delivery, the truck enters a docking area for loading.As goods are loaded into the truck, the information regarding the goodsis down-loaded into the storage terminal 3031 via the terminal 3007 orcode reader 3009 (FIG. 28a) via the premises or peripheral LANcommunications. This loading might also be accomplished automatically asthe forklift 3014 comes into range of the delivery truck 3033,establishes or joins the peripheral LAN, and transmits the previouslycollected data as described above in relation to FIG. 28a. Alternately,loading might also be accomplished via the premises LAN.

As information regarding a good is received and stored, the storageterminal 3031 might also request further information regarding any orall of the goods via the peripheral LAN's link to the host computer 3011through the premises LAN. More likely however, the storage terminal 3031if appropriately configured would participate on the premises LAN tocommunicate directly with the host computer 3011 to retrieve suchinformation.

The peripheral LAN base station 3021 if located on the dock couldprovide a direct low power peripheral LAN connection to the backbone LAN3019 and to the host computer 3011. Specifically, in one embodiment, thebase station 3021 is located on the dock and comprises a low power("short hop") radio operating in a frequency hopping mode over a 902-928MHz frequency band. However, the base station 3021 can instead beconfigured to communicate using, for example, infrared, UHF, 2.4 GHz or902 MHz spread spectrum direct sequence frequencies.

Once fully loaded and prior to leaving the dock, the storage device 3031may generate a printout of the information relating to the loaded goodsvia a peripheral LAN established with the printer 3013 on the dock. Inaddition, the information may be transmitted via the peripheral LANmodem 3023 to a given destination site.

As illustrated in FIG. 28c, once the storage terminal 3031 and hand-heldterminal 3007 moves out of range of the premises and peripheral LANs,i.e., the truck 3033 drives away from the dock, the vehicular LAN canonly gain access to the premises LAN via the more costly radio WANcommunication. Thus, although the storage terminal 3031 might only beconfigured with relaying control point functionality, to minimize radioWAN communication, the storage terminal 3031 can be configured to storerelatively large amounts of information and to provide processing power.Thus, the terminal 3007 can access such information and processing powerwithout having to access devices on the premises LAN via the radio WAN.

Upon reaching the destination, the storage terminal 3031 may participatein any in range peripheral and premises LAN at the delivery site dock.Specifically, as specific goods are unloaded, they are scanned fordelivery verification, preventing delivery of unwanted goods. The driveris also informed if goods that should have been delivered are still inthe truck. As this process takes place, a report can also be generatedvia a peripheral or premises LAN printer at the destination dock forreceipt signature. Similarly, the peripheral LAN modem on thedestination dock can relay the delivery information back to the hostcomputer 3011 for billing information or gather additional informationneeded, avoiding use of the radio WAN.

If the truck 3033 is used for service purposes, the truck 3033 leavesthe dock in the morning with the addresses and directions of the servicedestinations, technical manuals, and service notes which have beenselectively downloaded from the host computer 3011 via either thepremises or peripheral LAN to the storage terminal 3031 which may beconfigured with a hard drive and substantial processing power. Uponpulling out of range, the storage terminal 3031 and the computerterminal 3007 automatically form an independent, detached vehicular LAN.Alternately, the terminals 3007 and 3031 may have previously formed thevehicular LAN before leaving dock. In one embodiment, the vehicular LANoperates using frequency hopping protocol much the same as that of thepremises LAN, with the storage terminal 3031 acting much like thepremises LAN base stations. Thus, the radio transceiver circuitry forthe premises LAN participation may also be used for the vehicular LANand, as detailed above, a peripheral LAN. Similarly, if the radio WANchosen has similar characteristics, it may to be incorporated into asingle radio transceiver.

At each service address, the driver collects information using theterminal 3007 either as the data is collected, if within vehicular LANtransmission range of the storage terminal 3031, or as soon as theterminal 3007 comes within range. Any stored information within storageterminal 3031 may be requested via the vehicular LAN by the hand-heldterminal 3007. Information not stored within the vehicular LAN may becommunicated via a radio WAN as described above.

Referring again to FIG. 28b, upon returning to the dock, the storageterminal 3031, also referred to herein as a vehicle terminal, joins inor establishes a peripheral LAN with the peripheral LAN devices on thedock, if necessary. Communication is also established via the premisesLAN. Thereafter, the storage terminal 3031 automatically transfers theservice information to the host computer 3011 which uses the informationfor billing and in formulating service destinations for automaticdownloading the next day.

FIG. 29 is a diagrammatic illustration of another embodiment using aperipheral LAN to support roaming data collection by an operatoraccording to the present invention. As an operator 3061 roams thewarehouse floor he carries with him a peripheral LAN comprising theterminal 3007, code reader 3009 and a portable printer 3058. Theoperator collects information regarding goods, such as the box 3010,with the code reader 3009 and the terminal 3007. If the power resourcesare equal, the terminal 3007 may be configured and designated to alsoparticipate in the premises LAN.

Corresponding information to the code data must be retrieved from thehost computer 3011. The collected code information and retrievedcorresponding information can be displayed on the terminal 3007. Afterviewing for verification, the information can be printed on the printer3058. Because of this data flow requirement, the computer terminal 3007is selected as the peripheral LAN device which must also carry theresponsibility of communicating with the premises LAN.

If during collection, the operator decides to power down the computerterminal 3007 because it is not needed, the peripheral LAN becomesdetached from the premises LAN. Although it might be possible for thedetached peripheral LAN to function, all communication with the hostcomputer 3011 through the premises LAN is placed in a queue awaitingreattachment. As soon as the detached peripheral LAN comes within rangeof an attached peripheral LAN device, i.e., a device attached to thepremises LAN, the queued communications are relayed to the host. Itshould be clear from this description that the peripheral LAN may roamin relation to a device attached to the premises LAN ("premises LANdevice"). Similarly, the premises LAN device may roam in relation to theperipheral LAN. The roaming constitutes a relative positioning.Moreover, whenever a peripheral LAN and a master device move out ofrange of each other, the peripheral LAN may either poll for or scan foranother master device for attachment. The master device may constitute apremises LAN device, yet need not be.

To avoid detachment when the terminal 3007 is powered down, the codereader 3009 may be designated as a backup to the terminal 3007 forperforming the higher power communication with the premises LAN. Asdescribed in more detail below in reference to FIG. 33c regarding theidle sense protocol, whenever the code reader 3009 determines that theterminal 3007 has stopped providing access to the premises LAN, the codereader 3009 will take over the role if it is next in line to perform thebackup service. Thereafter, when the computer terminal 3007 is poweredup, it monitors the peripheral LAN channel, requests and regains fromthe code reader 3009 the role of providing an interface with thepremises LAN. This, however, does not restrict the code reader 3009 fromaccessing the premises LAN although the reader 3009 may choose to usethe computer terminal 3007 for power conservation reasons.

In addition, if the computer terminal 3007 reaches a predetermined lowbattery threshold level, the terminal 3007 will attempt to pass theburden of providing premises LAN access to other peripheral LAN backupdevices. If no backup device exists in the current peripheral LAN, thecomputer terminal 3007 may refuse all high power transmissions to thepremises LAN. Alternatively, the computer terminal 3007 may eitherrefuse predetermined select types of requests, or prompt the operatorbefore performing any transmission to the premises LAN. However, thecomputer terminal 3007 may still listen to the communications from thepremises LAN and inform peripheral LAN members of waiting messages.

FIG. 30 is a block diagram illustrating the functionality of RFtransceivers built in accordance with the present invention. Althoughpreferably plugging into PCMCIA slots of the computer terminals andperipherals, the transceiver 3110 may also be built-in or externallyattached via available serial, parallel or ethernet connectors forexample. Although the transceivers used by potential peripheral LANmaster devices may vary from those used by peripheral LAN slave devices(as detailed below), they all contain the illustrated functional blocks.

In particular, the transceiver 3110 contains a radio unit 3112 whichattaches to an attached antenna 3113. The radio unit 3112 used inperipheral LAN slave devices need only provide reliable low powertransmissions, and are designed to conserve cost, weight and size.Potential peripheral LAN master devices not only require the ability tocommunicate with peripheral LAN slave devices, but also require higherpower radios to also communicate with the premises LAN. Thus, potentialperipheral LAN master devices and other non-peripheral LAN slave devicesmight contain two radio units 3112 or two transceivers 3110--one servingthe premises LAN and the other serving the peripheral LAN--else onlycontain a single radio unit to service both networks.

In embodiments where cost and additional weight is not an issue, a dualradio unit configuration for potential peripheral LAN master devices mayprovide several advantages. For example, simultaneous transceiveroperation is possible by choosing a different operating band for eachradio. In such embodiments, a 2.4 GHz radio is included for premises LANcommunication while a 27 MHz radio supports the peripheral LAN.Peripheral LAN slave devices receive only the 27 MHz radio, while thenon-potential peripheral LAN participants from the premises LAN arefitted with only the 2.4 GHz radios. Potential peripheral LAN masterdevices receive both radios. The low power 27 MHz peripheral LAN radiois capable of reliably transferring information at a range ofapproximately 40 to 100 feet asynchronously at 19.2 KBPS. An additionalbenefit of using the 27 MHz frequency is that it is an unlicensedfrequency band. The 2.4 GHz radio provides sufficient power (up to 1Watt) to communicate with other premises LAN devices. Another benefit ofchoosing 2.4 GHz or 27 MHz bands is that neither require FCC licensing.Many different frequency choices could also be made such as the 900 MHzband, UHF, etc. Alternatively, infrared communication may be used insituations where line of sight may be achieved between devices on thenetwork.

In embodiments where cost and additional weight are at issue, a singleradio unit configuration is used for potential peripheral LAN masterdevices. Specifically, in such embodiments, a dual mode 2.4 GHz radiosupports both the peripheral LAN and premises LANS. In a peripheral LANmode, the 2.4 GHz radio operates at a single frequency, low power level(sub-milliwatt) to support peripheral LAN communication at relativelyclose distances 20-30 feet). In a high power (up to 1 Watt) or mainmode, the 2.4 GHz radio provides for frequency-hopping communicationover relatively long distance communication connectivity with thepremises LAN. Although all network devices might be fitted with such adual mode radio, only peripheral LAN master devices use both modes.Peripheral LAN slave devices would only use the low power mode while allother premises LAN devices would use only the high power mode. Becauseof this, to save cost, peripheral LAN slave devices are fitted with asingle mode radio operating in the peripheral LAN mode. Non-peripheralLAN participants are also fitted with a single mode (main mode) radiounit for cost savings.

Connected between the radio unit 3112 and an interface 3110, amicroprocessor 3120 controls the information flow through thetransceiver 3110. Specifically, the interface 3115 connects thetransceiver 3110 to a selected computer terminal, a peripheral device orother network device. Many different interfaces 3115 are used and thechoice will depend upon the connection port of the device to which thetransceiver 3110 will be attached. Virtually any type of interface 3110could be adapted for use with the transceiver 3110 of the presentinvention. Common industry interface standards include RS-232, RS-422,RS-485, 10BASE2 Ethernet, 10BASE5 Ethernet, 10BASE-T Ethernet, fiberoptics, IBM 4/16 Token Ring, V.11, V.24, V.35, Apple Localtalk andtelephone interfaces. In addition, via the interface 3115, themicroprocessor 3120 maintains a radio independent, interface protocolwith the attached network device, isolating the attached device from thevariations in radios being used.

The microprocessor 3120 also controls the radio unit 3112 to accommodatecommunication with either the premises LAN, the peripheral LAN, or both(for dual mode radios). Moreover, the same radio might also be used forvehicular LAN and radio WAN communication as described above. Forexample, a radio located in a vehicle or in a hand held terminal can beconfigured to communicate not only within a local network, but mightalso be capable of receiving paging messages.

More specifically, in a main mode transceiver, the microprocessor 3120utilizes a premises LAN protocol to communicate with the premises LAN.Similarly, in a peripheral LAN mode transceiver, the microprocessor 3120operates pursuant to a peripheral LAN protocol to communicate in theperipheral LAN. In the dual mode transceiver, the microprocessor 3120manages the use of and potential conflicts between both the premises andperipheral LAN protocols. Detail regarding the premises and peripheralLAN protocols can be found in reference to FIGS. 33-36 below.

In addition, as directed by the corresponding communication protocol,the microprocessor 3120 controls the power consumption of the radio3112, itself and the interface 3115 for power conservation. This isaccomplished in two ways. First, the peripheral LAN and premisesprotocols are designed to provide for a low power mode or sleep modeduring periods when no communication involving the subject transmitteris desired as described below in relation to FIGS. 33-34. Second, bothprotocols are designed to adapt in both data rate and transmission powerbased on power supply (i.e., battery) parameters and range informationas described in reference to FIGS. 35-36.

In order to insure that the proper device is receiving the informationtransmitted, each device is assigned a unique address. Specifically, thetransceiver 3110 can either have a unique address of its own or can usethe unique address of the device to which it is attached. The uniqueaddress of the transceiver can either be one selected by the operator orsystem designer or one which is permanently assigned at the factory suchas an IEEE address. The address 3121 of the particular transceiver 3110is stored with the microprocessor 3120.

In the illustrated embodiments of FIGS. 28-29, the peripheral LAN masterdevice is shown as being either a peripheral LAN base station or amobile or portable computer terminal. From a data flow viewpoint, inconsidering the fastest access through the network, such choices for theperipheral LAN master devices appear optimal. However, any peripheralLAN device might be assigned the role of the master, even those that donot seem to provide an optimal data flow pathway but may provide foroptimal battery usage. For example, in the personal peripheral LAN ofFIG. 29, because of the support from the belt 3059, the printer mightcontain the greatest battery capacity of the personal peripheral LANdevices. As such, the printer might be designated the peripheral LANmaster device and be fitted with either a dual mode radio or two radiosas master devices require. The printer, or other peripheral LAN slavedevices, might also be fitted with such required radios to serve only asa peripheral LAN master backup. If the battery power on the actualperipheral LAN master, i.e., the hand-held terminal 3007 (FIG. 29),drops below a preset threshold, the backup master takes over.

FIG. 31 is a drawing which illustrates an embodiment of the personalperipheral LAN shown in FIG. 29 which designates a printer as theperipheral LAN master device. Specifically, in a personal peripheral LAN3165, a computer terminal 3170 is strapped to the forearm of theoperator. A code reader 3171 straps to the back of the hand of the userand is triggered by pressing a button 3173 with the thumb. Because oftheir relatively low battery energy, the computer terminal 3170 and codereader 3171 are designated peripheral LAN slave devices and each containa peripheral LAN transceiver having a broadcast range of two meters orless. Because of its greater battery energy, the printer 3172 contains adual mode radio and is designated the peripheral LAN master device.

FIG. 32 is a block diagram illustrating a channel access algorithm usedby peripheral LAN slave devices according to the present invention. At ablock 3181, when a slave device has a message to send, it waits for anidle sense message to be received from the peripheral LAN master deviceat a block 3183. When an idle sense message is received, the slavedevice executes a back-off protocol at a block 3187 in an attempt toavoid collisions with other slave devices waiting to transmit.Basically, instead of permitting every slave device from repeatedlytransmitting immediately after an idle sense message is received, eachwaiting slave is required to first wait for a pseudo-random time periodbefore attempting a transmission. The pseudo-random back-off time periodis generated and the waiting takes place at a block 3187. At a block3189, the channel is sensed to determine whether it is clear fortransmission. If not, a branch is made back to the block 3183 to attempta transmission upon receipt of the next idle sense message. If thechannel is still clear, at a block 3191, a relatively small "request tosend" type packet is transmitted indicating the desire to send amessage. If no responsive "clear to send" type message is received fromthe master device, the slave device assumes that a collision occurred ata block 3193 and branches back to the block 3183 to try again. If the"clear to send" message is received, the slave device transmits themessage at a block 3195.

Several alternate channel access strategies have been developed forcarrier sense multiple access (CSMA) systems and include 1-persistent,non-persistent and p-persistent. Such strategies or variations thereofcould easily be adapted to work with the present invention.

FIG. 33a is a timing diagram of the protocol used according to oneembodiment the present invention illustrating a typical communicationexchange between a peripheral LAN master device having virtuallyunlimited power resources and a peripheral LAN slave device. Time line3201 represents communication activity by the peripheral LAN masterdevice while time line 3203 represents the corresponding activity by theperipheral LAN slave device. The master periodically transmits an idlesense message 3205 indicating that it is available for communication orthat it has data for transmission to a slave device. Because the masterhas virtually unlimited power resources, it "stays awake" for the entiretime period 3207 between the idle sense messages 3205. In other words,the master does not enter a power conserving mode during the timeperiods 3207.

The slave device uses a binding protocol (discussed below with regard toFIG. 33c) to synchronize to the master device so that the slave mayenter a power conserving mode and still monitor the idle sense messagesof the master to determine if the master requires servicing. Forexample, referring to FIG. 33a, the slave device monitors an idle sensemessage of the master during a time period 3209, determines that noservicing is required, and enters a power conserving mode during thetime period 3211. The slave then activates during a time period 3213 tomonitor the next idle sense message of the master. Again, the slavedetermines that no servicing is required and enters a power conservingmode during a time period 3215. When the slave activates again during atime period 3217 to monitor the next idle sense message, it determinesfrom a "request to send" type message from the master that the masterhas data for transmission to the slave. The slave responds by sending a"clear to send" type message during the time period 3217 and staysactivated in order to receive transmission of the data. The master isthus able to transmit the data to the slave during a time period 3219.Once the data is received by the slave at the end of the time period3221, the slave again enters a power conserving mode during a timeperiod 3223 and activates again during the time period 3225 to monitorthe next idle sense message.

Alternatively, the slave may have data for transfer to the master. Ifso, the slave indicates as such to the master by transmitting a messageduring the time period 3217 and then executes a backoff algorithm todetermine how long it must wait before transmitting the data. The slavedetermines from the backoff algorithm that it must wait the time period3227 before transmitting the data during the time period 3221. The slavedevices use the backoff algorithm in an attempt to avoid the collisionof data with that from other slave devices which are also trying tocommunicate with the master. The backoff algorithm is discussed morefully above in reference to FIG. 32.

The idle sense messages of the master may also aid in schedulingcommunication between two slave devices. For example, if a first slavedevice has data for transfer to a second slave device, the first slavesends a message to the master during the time period 3209 requestingcommunication with the second slave. The master then broadcasts therequest during the next idle sense message. Because the second slave ismonitoring the idle sense message, the second slave receives the requestand stays activated at the end of the idle sense message in order toreceive the communication. Likewise, because the first slave is alsomonitoring the idle sense message, it too receives the request and staysactivated during the time period 3215 to send the communication.

FIG. 33b is a timing diagram of the protocol used according to oneembodiment of the present invention illustrating a typical communicationexchange between a peripheral LAN master having limited power resourcesand a peripheral LAN slave device. This exchange is similar to thatillustrated in FIG. 33a except that, because it has limited powerresources, the master enters a power conserving mode. Beforetransmitting an idle sense message, the master listens to determine ifthe channel is idle. If the channel is idle, the master transmits anidle sense message 3205 and then waits a time period 3231 to determineif any devices desire communication. If no communication is desired, themaster enters a power conserving mode during a time period 3233 beforeactivating again to listen to the channel. If the channel is not idle,the master does not send the idle sense message and enters a powersaving mode for a time period 3235 before activating again to listen tothe channel.

Communication between the master and slave devices is the same as thatdiscussed above in reference to FIG. 33a except that, after sending orreceiving data during the time period 3219, the master device enters apower conserving mode during the time period 3237.

FIG. 33c is also a timing diagram of one embodiment of the protocol usedaccording to the present invention which illustrates a scenario whereinthe peripheral LAN master device fails to service peripheral LAN slavedevices. The master device periodically sends an idle sense message3205, waits a time period 3231, and enters a power conserving modeduring a time period 3233 as discussed above in reference to FIG. 33b.Similarly, the slave device monitors the idle sense messages during timeperiods 3209 and 3213 and enters a power conserving mode during timeperiods 3211 and 3215. For some reason, however, the master stopstransmitting idle sense messages. Such a situation may occur, forexample, if the master device is portable and is carried outside therange of the slave's radio. During a time period 3241, the slaveunsuccessfully attempts to monitor an idle sense message. The slave thengoes to sleep for a time period 3243 and activates to attempt to monitora next idle sense message during a time period 3245, but is againunsuccessful.

The slave device thereafter initiates a binding protocol to attempt toregain synchronization with the master. While two time periods 3241 and3245 are shown, the slave may initiate such a protocol after any numberof unsuccessful attempts to locate an idle sense message. With thisprotocol, the slave stays active for a time period 3247, which is equalto the time period from one idle sense message to the next, in anattempt to locate a next idle sense message. If the slave is againunsuccessful, it may stay active until it locates an idle sense messagefrom the master, or, if power consumption is a concern, the slave mayenter a power conserving mode at the end of the time period 3247 andactivate at a later time to monitor for an idle sense message.

In the event the master device remains outside the range of the slavedevices in the peripheral LAN for a period long enough such thatcommunication is hindered, one of the slave devices may take over thefunctionality of the master device. Such a situation is useful when theslave devices need to communicate with each other in the absence of themaster. Preferably, such a backup device has the ability to communicatewith devices on the premises LAN. If the original master returns, itlistens to the channel to determine idle sense messages from the backup,indicates to the backup that it has returned and then begins idle sensetransmissions when it reestablishes dominance over the peripheral LAN.

FIG. 34 is a timing diagram illustrating one embodiment of theperipheral LAN master device's servicing of both the high poweredpremises LAN and the low powered peripheral LAN subnetwork, with asingle or plural radio transceivers, in accordance with presentinvention. Block 3251 represents typical communication activity of themaster device. Line 3253 illustrates the master's communication with abase station on the premises LAN while line 3255 illustrates themaster's communication with a slave device on the peripheral LAN. Lines3257 and 3259 illustrate corresponding communication by the base stationand slave device, respectively.

The base station periodically broadcasts HELLO messages 3261 indicatingthat it is available for communication. The master device monitors theHELLO messages during a time period 3263, and, upon determining that thebase does not need servicing, enters a power conserving mode during atime period 3265. The master then activates for a time period to monitorthe next HELLO message from the base. If the master has data to send tothe base, it transmits the data during a time period 3271. Likewise, ifthe base has data to send to the master, the base transmits the dataduring a time period 3269. Once the data is received or sent by themaster, it may again enter a power conserving mode. While HELLO messageprotocol is discussed, a number of communication protocols may be usedfor communication between the base and the master device. As may beappreciated, the peripheral LAN master device acts as a slave to basestations in the premises LAN.

Generally, the communication exchange between the master and the slaveis similar to that described above in reference to FIG. 33b. Block 3273,however, illustrates a situation where the master encounters acommunication conflict, i.e., it has data to send to or receive from theslave on the peripheral LAN at the same time it will monitor thepremises LAN for HELLO messages from the base. If the master has tworadio transceivers, the master can service both networks. If, however,the master only has one radio transceiver, the master chooses to serviceone network based on network priority considerations. For example, inblock 3273, it may be desirable to service the slave because of thepresence of data rather than monitor the premises LAN for HELLO messagesfrom the base. On the other hand, in block 3275, it may be moredesirable to monitor the premises LAN for HELLO messages rather thantransmit an idle sense message on the peripheral LAN.

FIGS. 35 and 36 are block diagrams illustrating additional power savingfeatures according to the present invention, wherein ranging and batteryparameters are used to optimally select the appropriate data rate andpower level for subsequent transmissions. Specifically, even thoughnetwork devices such as the computer terminal 3007 in FIGS. 28-29 havethe capability of performing high power transmissions, because ofbattery power concerns, such devices are configured to utilize minimumtransmission energy. Adjustments are made based on ranging informationand on battery parameters. Similarly, within the peripheral LAN, eventhough lower power transceivers are used, battery conservation issuesalso justify the use of such data rate and power adjustments. Thisprocess is described in more detail below in reference to FIGS. 35 and36.

More specifically, FIG. 35 is a block diagram which illustrates aprotocol 3301 used by a destination peripheral LAN device and acorresponding protocol 3303 used by a source peripheral LAN device toadjust the data rate and possibly the power level for futuretransmission between the two devices. At a block 3311, upon receiving atransmission from a source device, the destination device identifies arange value at a block 3313. In a low cost embodiment, the range valueis identified by considering the received signal strength indications(RSSI) of the incoming transmission. Although RSSI circuitry might beplaced in all peripheral LAN radios, the added expense may require thatonly peripheral LAN master devices receive the circuitry. This wouldmean that only peripheral LAN master devices would perform the functionof the destination device. Other ranging techniques or signal qualityassessments can also be used, such as measuring jitter in receivedsignals, by adding additional functionality to the radios. Finally,after identifying the range value at the block 3313, the destinationdevice subsequently transmits the range value to the slave device fromwhich the transmission was received, at a block 3314.

Upon receipt of the range value from the destination device at a block3321, the source peripheral LAN device evaluates its battery parametersto identify a subsequent data rate for transmission at a block 3323. Ifrange value indicates that the destination peripheral LAN device is verynear, the source peripheral LAN device selects a faster data rate. Whenthe range value indicates a distant master, the source device selects aslower rate. In this way, even without adjusting the power level, thetotal energy dissipated can be controlled to utilize only that necessaryto carry out the transmission. However, if constraints are placed on themaximum or minimum data rates, the transmission power may also need tobe modified. For example, to further minimize the complexity associatedwith a fully random range of data rate values, a standard range and setof several data rates may be used. Under such a scenario, a transmissionpower adjustment might also need to supplement the data rate adjustment.Similarly, any adjustment of power must take into consideration maximumand minimum operable levels. Data rate adjustment may supplement suchlimitations. Any attempted modification of the power and data rate mighttake into consideration any available battery parameters such as thosethat might indicate a normal or current battery capacity, the drain onthe battery under normal conditions and during transmission, or the factthat the battery is currently being charged. The latter parameter provesto be very significant in that when the battery is being charged, theperipheral LAN slave device has access to a much greater power sourcefor transmission, which may justify the highest power transmission andpossibly the slowest data rate under certain circumstances.

Finally, at a block 3325, an indication of the identified data rate istransmitted back to the destination device so that future transmissionsmay take place at the newly selected rate. The indication of data ratemay be explicit in that a message is transmitted designating thespecific rate. Alternately, the data rate may be transferred implicitlyin that the new rate is chose and used by the source, requiring thedestination to adapt to the change. This might also be done using apredefined header for synchronization.

In addition, at the block 3325, in another embodiment, along with theindication of the identified data rate, priority indications are also becommunicated. Whenever battery power is detected as being low, a radiotransmits a higher priority indication, and each receiver thereaftertreats the radio as having a higher protocol priority than other suchradios that exhibit normal power supply energy. Thus, the remainingbattery life is optimized. For example, in a non-polling network, thelow power device might be directly polled periodically so to allowscheduled wake-ups and contention free access to a receiver. Similarly,in an alternate embodiment, priority indications not need to be sent.Instead, the low battery power device itself exercises protocolpriority. For example, for channel access after detecting that thechannel is clear at the end of an ongoing transmission, devices withnormal energy levels are required to undergo a pseudo-random back-offbefore attempting a transmission (to avoid collision). The low powerdevice may either minimize the back-off period or ignore the back-offperiod completely. Thus, the low power device gains channel accesseasier than other normal power level devices. Other protocol priorityschemes may also be assigned by the receivers to the low power device(via the indication), else may be taken directly by the low powerdevice.

FIG. 36 illustrates an alternate embodiment for carrying out the datarate and possibly power level adjustment. At a block 3351 upon bindingand possibly periodically, the source peripheral LAN device sends anindication of its current battery parameters to the destinationperipheral LAN device. This indication may be each of the parameters ormay be an averaged indication of all of the parameters together. At ablock 3355, upon receipt, the destination peripheral LAN device 355stores the battery parameters (or indication). Finally, at a block 3358,upon receiving a transmission from the source device, based on rangedeterminations and the stored battery parameters, the destinationterminal identifies the subsequent data rate (and possibly power level).Thereafter, the new data rate and power level are communicated to thesource device either explicitly or implicitly for future transmissions.

FIG. 37 illustrates an exemplary block diagram of a radio unit 3501capable of concurrent participation on multiple LAN's. To transmit, acontrol processor 3503 sends a digital data stream to a modulationencoding circuit 3505. The modulation encoding circuit 3505 encodes thedata stream in preparation for modulation by frequency translationcircuit 3507. The carrier frequency used to translate the data stream isprovided by a frequency generator circuit 3509. Thereafter, themodulated data stream is amplified by a transmitter amplifier circuit3511 and then radiated via the one of a plurality of antennas 3513 thathas been selected via an antenna switching circuit 3515. Together, themodulation encoding circuitry 3505, translator 3507, amplifier 3511 andassociated support circuitry constitute the transmitter circuitry.

Similarly, to receive data, the RF signal received by the selected oneof the plurality of antennas 3513 is communicated to a receiver RFprocessing circuit 3517. After performing a rather coarse frequencyselection, the receiver RF processing circuit 3517 amplifies the RFsignal received. The amplified received signal undergoes a frequencyshift to an IF range via a frequency translation circuit 3519. Thefrequency translation circuit 3519 provides the center frequency for thefrequency shift. Thereafter, a receiver signal processing circuitreceives the IF signal, performs a more exact channel filtering anddemodulation, and forwards the received data to the control processor3503, ending the process. Together, the receiver signal processing 3521,translator 3517, receiver RF processing 3517 and associated supportcircuitry constitute the receiver circuitry.

The control processor 3503 operates pursuant to a set of softwareroutines stored in memory 3522 which may also store incoming andoutgoing data. Specifically, the memory 3522 contains routines whichdefine a series of protocols for concurrent communication on a pluralityof LANs. As part of such operation, the control processor 3503 providesfor power savings via a power source control circuit 3523, i.e.,whenever the participating protocols permit, the control processor 3503causes selective power down of the radio transceiver circuitry via acontrol bus 3525. Also via the bus 3525, the control processor sets thefrequency of the frequency generator 3509 so as to select theappropriate band and channel of operation required by a correspondinglyselected protocol. Similarly, the control processor 3503 selects theappropriate antenna (via the antenna switching circuitry 3515) andchannel filtering in preparation for operation on a selected LAN.Responding to the software routines stored in the memory 3522, thecontrol processor 3503 selects the appropriate LANs to establishparticipation, detaches from those of the selected LANs in whichparticipation is no longer needed, identifies from the selected LANs acurrent priority LAN in which to actively participate, maintains atime-shared servicing of the participating LANs. Further detailregarding this process follows below.

In one embodiment, the control processor 3503 constitutes a typicalmicroprocessor on an independent integrated circuit. In anotherembodiment, the control processor 3503 comprises a combination ofdistributed processing circuitry which could be included in a singleintegrated circuit as is a typical microprocessor. Similarly, the memory3522 could be any type of memory unit(s) or device(s) capable ofsoftware storage.

The radio circuitry illustrated is designed with the frequency nimblefrequency generator 3509 so as to be capable of operation on a pluralityof LANs/WANs. Because each of the plurality may be allocated differentfrequency bands, more than one antenna may be desirable (although asingle antenna could be used, antenna bandwidth limitations might resultin an unacceptable transmission-reception inefficiency). Thus, to selectthe appropriate configuration, the control processor 3503 firstidentifies the LAN/WAN on which to participate and selects thecorresponding radio configuration parameters from the memory 3521.Thereafter, using the configuration parameters and pursuant to controlroutines stored in the memory 3522, the control processor 3503 sets thefrequency of the generator 3509, selects the appropriate antenna via theantenna switching circuit 3515, and configures the receiver RF andsignal processing circuits 3517 and 3521 for the desired LAN/WAN.

More particularly, the antenna switching circuit 3515 comprises aplurality of digitally controlled switches, each of which is associatedwith one of the plurality of antennas 3513 so as to permit selectiveconnection by the control processor 3503 of any available antenna to thetransceiver circuitry.

FIG. 38 illustrates an exemplary functional layout of the frequencygenerator 3509 of FIG. 37 according to one embodiment of the presentinvention. Basically, the frequency generator 3509 responds to thecontrol processor 3503 by producing the translation frequency necessaryfor a selected LAN/WAN. The illustrated frequency generator comprises avoltage controlled oscillator (VCO) 3601. As is commonly known, for aVCO, the center frequency F_(VCO) tracks the input voltage. However,because typical VCO's are subject to drift, the VCO is stabilized byconnecting it in a phase locked loop to a narrowband reference, such asa crystal reference oscillator 3603. The oscillator 3603 outputs asignal of a fixed or reference frequency F_(REF) to a divide-by-Rcircuit 3605, which divides as its name implies the reference frequencyF_(REF) by the known number R. A phase detector 3609 receives thedivided-by-R output of the circuit 3609 and the feedback from the outputof the VCO 3601 via a divide-by-N circuit 3607. Upon receipt, the phasedetector 3609 compares the phase of the outputs from the circuits 3605and 3607. Based on the comparison, a phase error signal is generated andapplied to a low-pass loop filter 3611. The output of the filter 3611 isapplied to the input of the VCO 3601 causing the center frequency of theVCO 3601 to lock-in. Therefore, if the output of the VCO 3601 begins todrift out of phase of the reference frequency, the phase detector 3609responds with a corrective output so as to adjust the center frequencyof the VCO 3601 back in phase.

With the illustrated configuration, the center frequency of the VCO 3601is a function of the reference frequency as follows:

    F.sub.VCO =(FEF * N) / R

Thus, to vary the center frequency of the VCO 3601 to correspond to aband of a selected LAN/WAN in which active participation is desired, thecontrol processor 3503 (FIG. 37) need only vary the variables "R" and"N" and perhaps the frequency of the reference oscillator. Because theoutput F_(REF) of the reference oscillator 3603 is quite stable, thephase lock loop as shown also keeps the output frequency F_(VCO) of theVCO 3601 stable.

More specifically, although any other scheme might be implemented, thevalue R in the divide-by-R circuit 3605 is chosen so as to generate anoutput equal to the channel spacing of a desired LAN/WAN, while thevalue N is selected as a multiplying factor for stepping up the centerfrequency of the VCO 3601 to the actual frequency of a given channel.Moreover, the frequency of the reference oscillator is chosen so as tobe divisible by values of R to yield the channel spacing frequencies ofall potential LANs and WANs. For example, to participate on both MTELCorporation's Two Way Paging WAN (operating at 900 MHz with 25 KHz and50 KHz channel spacings) and ARDIS Corporation's 800 MHz specializedmobile radio (SMR) WAN (operating at 25 KHz channel spacings centered atmultiples of 12.5 KHz), a single reference frequency may chosen to be awhole multiple of 12.5 KHz. Alternately, multiple reference frequenciesmay be chosen. Moreover, the value N is chosen to effectively multiplythe output of the divide-by-R circuit 3605 to the base frequency of agiven channel in the selected WAN.

For frequency hopping protocols, the value of R is chosen so as to yieldthe spacing between frequency hops. Thus, as N is incremented, eachhopping frequency can be selected. Randomizing the sequence of suchvalues of N provides a hopping sequence for use by a base station asdescribed above. Pluralities of hopping sequences (values of N) may bestored in the memory 3522 (FIG. 37) for operation on the premises LAN,for example.

In addition to the single port phase locked loop configuration for thefrequency generator 3509, other configurations might also beimplemented. Exemplary circuitry for such configurations can be found incopending U.S. patent application Ser. No. 08/205,639, filed Mar. 4,1994 by Mahany et al., now U.S. Pat. No. 5,555,276, entitled "Method ofand Apparatus For Controlling Modulation of Digital Signals inFrequency-Modulated Transmissions". This application is incorporatedherein in its entirety.

FIG. 39 illustrates further detail of the receiver RF processing circuit3517 of FIG. 37 according to one embodiment of the present invention.Specifically, a preselector 3651 receives an incoming RF data signalfrom a selected one of the plurality of antennas 3513 (FIG. 37) via aninput line 3653. The preselector 3651 provides a bank of passive filters3657, such as ceramic or dielectric resonator filters, each of whichprovides a coarse filtering for one of the LAN/WAN frequencies to whichit is tuned. One of the outputs from the bank of passive filters 3657 isselected by the control processor 3503 via a switching circuit 3655 soas to monitor the desired one of the available LANs/WANs. Thereafter,the selected LAN/WAN RF signal is amplified by an RF amplifier 3659before translation by the frequency translation circuit 3519 (FIG. 37).

FIG. 40 illustrates further detail of the receiver signal processingcircuit 3521 of FIG. 37 according to one embodiment of the presentinvention. In particular, digitally controlled switching circuits 3701and 3703 respond to the control processor 3503 by selecting anappropriate pathway for the translated IF data signal through one of abank of IF filters 3705. Each IF filter is an analog crystal filter,although other types of filters such as a saw filter might be used. TheIF filters 3705 provide rather precise tuning to select the specificchannel of a given LAN/WAN.

After passing through the switching circuit 3703, the filtered IF datasignal is then amplified by an IF amplifier 3707. The amplified IFsignal is then communicated to a demodulator 3709 for demodulation. Thecontrol processor retrieves the incoming demodulated data signal forprocessing and potential storage in the memory 3522 (FIG. 37).

FIG. 41 illustrates further detail of the receiver signal processingcircuit 3521 of FIG. 37 according to another embodiment of the presentinvention. Specifically, the IF signal resulting from the translation bythe frequency translator circuitry 3519, enters the receiver signalprocessing circuit via an input 3751. Thereafter, the IF signal passesthrough an anti-aliasing filter 3753, and is amplified by a linearamplifier 3755. An IF oscillator 3757 supplies a reference signalf_(REF) for translation of the incoming IF signal at frequencytranslation circuits 3759 and 3761. A phase shift circuit 3763 providesfor a 90 degree shift of f_(REF), i.e., if f_(REF), is considered a SINEwave, then the output of the circuit 3763 is the COSINE of F_(REF). Boththe SINE and COSINE frequency translation pathways provide for channelselection of the incoming data signal. Thereafter the data signals arepassed through corresponding low pass filters 3765 and 3767 inpreparation for sampling by analog to digital (A/D) converters 3769 and3771. Each A/D converter forwards the sampled data to a digital signalprocessor 3773 which provides for further filtering and demodulation.The digital signal processor 3773 thereafter forwards the incoming datasignal to the control processor 3503 (FIG. 37) via an output line 3775.Moreover, although the digital signal processor 3773 and the controlprocessor 3507 are discrete components in the illustrated example, theymay also be combined into a single integrated circuit.

FIG. 42 illustrates further detail of some of the storage requirementsof the memory 3522 of FIG. 37 according to one embodiment of the presentinvention. To control the radio, the control processor 3503 (FIG. 37)accesses the information in the memory 3522 needed for radio setup andoperation on a plurality of LANs/WANs. Among other information, thememory 3522 stores: 1) a plurality of software protocols, one for eachLAN/WAN to be supported, which define how the radio is to participate onthe corresponding LAN; and 2) an overriding control set of routineswhich govern the selection, use and interaction of the plurality ofprotocols for participation on desired LANs/WANs.

Specifically, in the memory unit 3522, among other information androutines, software routines relating to the media access control (MAC)sublayer of the communication protocol layers can be found. In general,a MAC sulayer provides detail regarding how communication generallyflows through a corresponding LAN or WAN. Specifically, the MAC sublayerhandles functions such as media access control, acknowledge, errordetection and retransmission. The MAC layer is fairly independent of thespecific radio circuitry and channel characteristics of the LAN or WAN.

As illustrated, premises LAN, peripheral LAN, vehicular LAN and WAN MACroutines 3811, 3813, 3815 and 3817 provide definition as to how thecontrol processor 3503 (FIG. 37) should operate while activelyparticipating on each LAN or WAN. Although only the several sets of MACroutines are shown, many other sets might also be stored or down-loadedinto the memory 3522. Moreover, the sets of MAC routines 3811-17 mightalso share a set of common routines 3819. In fact, the sets of MACroutines 3811-17 might be considered a subset of an overall MAC whichshares the common MAC routines 3819.

Below the MAC layer in the communication hierarchy, hardware and channelrelated software routines and parameters are necessary for radiocontrol. For example, such routines govern the specific switching forchannel filtering and antenna selection required by a given LAN or WAN.Similarly, these routines govern the control processor 3503's selectionof parameters such as for R and N for the frequency generator 3509 (FIG.38), or the selective power-down (via the power source control circuitry3503--FIG. 37) of portions or all of the radio circuitry wheneverpossible to conserve battery power. As illustrated, such routines andparameters are referred to as physical (PHY) layer control software3821. Each of the sets of MAC routines 3811-17 and 3819 provide specificinteraction with the PHY layer control software 3821.

A set of MAC select/service routines 3823 govern the management of theoverall operation of the radio in the network. For example, ifparticipation on the premises LAN is desired, the MAC select/serviceroutines 3823 direct the control processor 3503 (FIG. 37) to the commonand premises MAC routines 3819 and 3811 respectively. Thereafter, ifconcurrent participation with a peripheral LAN is desired, theselect/service routines 3823 direct the control processor 3503 to entera sleep mode (if available). The control processor 3503 refers to thepremises LAN MAC routines 3811, and follows the protocol necessary toestablish sleep mode on the premises LAN. Thereafter, the select/serviceroutines 3823 directs the control processor 3503 to the peripheral LANMAC routines 3813 to establish and begin servicing the peripheral LAN.Whenever the peripheral LAN is no longer needed, the select/serviceroutines 3823 direct a detachment from the peripheral LAN (if required)as specified in the peripheral LAN MAC routines 3813. Similarly, ifduring the servicing of the peripheral LAN a overriding need to servicethe premises LAN arises, the processor 3503 is directed to enter a sleepmode via the peripheral LAN MAC routines 3813, and to return toservicing the premises LAN.

Although not shown, additional protocol layers as well as incoming andoutgoing data are also stored with the memory 3522, which, as previouslyarticulated, may be a distributed plurality of storage devices.

FIG. 43 illustrates a software flow chart describing the operation ofthe control processor 3503 (FIG. 37) in controlling the radio unit toparticipate on multiple LANs according to one embodiment of the presentinvention. Specifically, at a block 3901, the control processor firstdetermines whether the radio unit needs to participate on an additionalLAN (or WAN). If such additional participation is needed, at a block3903, the radio unit may register sleep mode operation with otherparticipating LANs if the protocols of those LANs so require and theradio unit has not already done so. Next, at a block 3905, the controlprocessor causes the radio unit to poll or scan to locate the desiredadditional LAN. If the additional LAN is located at a block 3907,participation of the radio unit on the additional LAN is established ata block 3909.

If additional participation is not needed at block 3901, or if theadditional LAN has not been located at block 3907, or once participationof the radio unit on the additional LAN has been established at block3909, the control processor next determines at a block 3911 whether anyof the participating LANs require servicing. If any given participatingLAN requires servicing, , at a block 3913, the radio unit may berequired by the protocol of the given LAN to reestablish an activeparticipation status on that LAN, i.e., indicate to the given LAN thatthe radio unit has ended the sleep mode. Next, at a block 3915, theradio unit services the given LAN as needed or until the servicing ofanother LAN takes priority over that of the given LAN. At a block 3917,the radio unit may then be required to register sleep mode operationwith the given LAN if the LAN's protocol so requires.

At that point, or if no participating LAN needs servicing at block 3911,the control processor determines at a block 3919 whether the radio needsto detach from any given participating LAN. If so, the radio unit mayimplicitly detach at a block 3923 if the protocol of the LAN from whichthe radio wishes to detach requires no action by the radio unit.However, at a block 3921, the radio unit may be required to establishactive participation on the LAN in order to explicitly detach at block3923. For example, such a situation may arise when a portable terminaldesires to operate on a shorter range vehicular LAN and detaches from apremises LAN. The portable terminal may be required by the protocol ofthe premises LAN to establish active communication on the premises LANto permit the radio unit to inform the premises LAN that it is detachingand can only be accessed through the vehicular LAN.

Once the radio unit is detached at block 3923, or if the radio unit doesnot need to detach from any participating LANs at block 3919, thecontrol processor returns to block 3901 to again determine whether theradio unit needs to participate on an additional LAN, and repeats theprocess.

FIG. 44 is an alternate embodiment of the software flow chart whereinthe control processor participates on a master LAN and, when needed, ona slave LAN. Specifically, at a block 3951, the control processor causesthe radio unit to poll or scan in order to locate the master LAN. If themaster LAN has not been located at a block 3953, polling or scanning forthe master LAN continues. Once the master LAN is located, participationwith the master is established at a block 3955. At a block 3957, theradio unit participates with the master LAN until the need for the radiounit to participate on the slave LAN takes precedence. When thatcondition occurs, the control processor determines at a block 3959whether participation of the radio unit on the slave network isestablished. If not, such participation is established at a block 3961.Next, at a block 3963, the radio unit services the slave LAN as neededor until the servicing of the master LAN takes priority. If the controlprocessor determines at a block 3965 that servicing of the slave LAN hasbeen completed, the radio unit detaches from the slave LAN at a block3967 and returns to block 3957 to continue participation on the masterLAN.

However, if the control processor determines at block 3965 thatservicing has not been, or may not be, completed, the radio unit doesnot detach from the slave LAN. In that case, before returning to block3957 to service the master LAN, the radio unit may be required by theprotocol of the slave LAN to register sleep mode operation with theslave LAN at a block 3969.

In another embodiment, shown in FIG. 45, the overall communicationsystem of the present invention has been adapted to service theenvironment found, for example, in a retail store. As illustrated, thepremises of the retail store are configured with a communication networkto provide for inventory control. Specifically, the communicationnetwork includes a backbone LAN 4501, a inventory computer 4511, and aplurality of cash registers located throughout the store, such as cashregisters 4503 and 4505. As illustrated, the backbone LAN 4501 is asingle wired link, such as Ethernet. However, it may be comprised ofmultiple sections of wired links with or without wireless linkinterconnects. For example, in another embodiment, each cash register4503 and 4505 is communicatively interconnected with the inventorycomputer via an infrared link.

The inventory computer 4511, which can range from a personal to mainframe computer, provides central control over the retail inventory bymonitoring the inventory status. Thus, the inventory computer 4511 mustmonitor both sales and delivery information regarding inventoried goods.To monitor sales information, the cash registers 4503 and 4505 includecode scanners, such as tethered code scanners 4507 and 4509, which readcodes on product labels or tags as goods are purchased. After receivingthe code information read from the scanners 4507 and 4509, the cashregisters 4503 and 4505 communicate sales information to the inventorycomputer 4511 via the backbone LAN 4501. To monitor deliveryinformation, when the truck 4513 makes a delivery, the informationregarding the goods delivered is communicated to the inventory computer4511 via the base station 4517. As illustrated, the base station 4517acts as a direct access point to the backbone LAN 4501, even though aseries of wireless hops might actually be required.

Upon receiving the sales information from the cash registers 4503 and4505, the inventory computer 4511 automatically debits the inventorycount of the goods sold. Similarly, upon receiving the deliveryinformation, the inventory computer 4511 automatically credits theinventory count of the goods delivered. With both the sales and deliveryinformation, the inventory computer 4511 accurately monitors theinventory of all goods stocked by the retail store. From the inventoryinformation, the inventory computer 4511 generates purchase orders forsubsequent delivery, automating the entire process.

In particular, the inventory computer 4511 receives sales informationfrom the cash registers 4503 and 4505 as detailed above. Whenever therestocking process is initiated, the inventory computer 4511 checks theretail inventory for each item sold to determine if restocking isneeded. If restocking proves necessary, the inventory computer 4511,evaluating recent sales history, determines the quantity of the goodsneeded. From this information, an "inventory request" is automaticallygenerated by the inventory computer 4511. Once verified (as modified ifneeded), the inventory request is automatically forwarded by theinventory computer 4511 to the warehouse 4519. This forwarding occursvia either a telephone link using a modem 4521, or a WAN link using thebackbone LAN 4501, base station 4517, and an antenna tower 4523.

At the remote warehouse 4519, the delivery truck 4513 is loaded pursuantto the inventory request received from the inventory computer 4511.After loading, the truck 4513 travels to the premises of the retailstore. When within range of the base station 4517, the radio terminal4515 in the truck 4513 automatically gains access to the retail premisesLAN via the base station 4517 (as detailed above), and communicates ananticipated delivery list (a "preliminary invoice"), responsive to theinventory request, to the inventory computer 4511. In response, dockworkers can be notified to prepare for the arrival of the delivery truck4513. In addition, any rerouting information can be communicated to theterminal 4515 in the delivery truck 4513. If a complete rerouting isindicated, the truck 4513 may be redirected without ever having reachedthe dock.

While unloading the delivery truck 4513, codes are read from all goodsas they are unloaded using portable code readers, which may be builtinto or otherwise communicatively attached to the radio terminal 4515.The codes read are compared with and debited against the preliminaryinvoice as the goods are unloaded. This comparing and debiting occurseither solely within the terminal 4515 or jointly within the terminal4515 and the inventory computer 4511. If the codes read do notcorrespond to goods on the inventory request, or if the codes read docorrespond but are in excess of what was required by the inventoryrequest, the goods are rejected. Rejection, therefore, occurs prior tothe actual unloading of the goods from the delivery truck 4513.

At the dock, the goods received from the delivery truck 4513 undergo aconfirmation process by a dock worker who, using a radio terminal 4525configured with a code reader, reads the codes from the goods on thedock to guarantee that the proper goods, i.e., those requested pursuantto the inventory request, were actually unloaded. This extra step ofconfirmation can be eliminated, however, where the dock worker directlyparticipates in the code reading during the unloading process in thedelivery truck 4513. Similarly, the code reading within the deliverytruck 4513 could be eliminated in favor of the above described on-dockconfirmation process, but, reloading of any wrongly unloaded goods wouldbe required.

Upon confirmation of the delivery by the dock worker, a verified invoiceis automatically generated by the radio terminal 4515 and routed to theinventory computer 4511 for inventory and billing purposes. In addition,the verified invoice is routed to the warehouse 4519. Such routing mayoccur as soon as the delivery truck returns to the warehouse 4519.However, to accommodate rerouting in situations where goods have beenturned away at the retail store, the radio terminal 4515 communicatesthe final invoice immediately to the warehouse 4519. The warehouse 4519,upon receiving the final invoice, checks the final invoice with the listof goods loaded in the delivery truck 4513, and determines whetherdelivery of the remaining goods is possible. If so, the warehouse 4519reroutes the truck 4513 to the next delivery site.

The communication of the final invoice and the rerouting informationbetween the warehouse 4519 and the terminal 4515 may utilize a low costcommunication pathway through the telephone link in the premises networkof the retail store. In particular, the pathway for such communicationutilizes the base station 4517, backbone LAN 4501, inventory computer4511 and modem 4521. Alternately, the communication pathway might alsoutilize the WAN directly from the radio terminal 4515 to the warehouse4519 via the antenna tower 4523. Moreover, the antenna tower 4523 ismerely representative of a backbone network for the WAN. Depending onthe specific WAN used, the tower 4523 may actually be comprised of aplurality of towers using microwave links to span the distance betweenthe retail premises and the warehouse 4519. Similarly, satelliterelaying of the communications might also be used.

Moreover, it will be apparent to one skilled in the art having read theforegoing that various modifications and variations of thiscommunication system according to the present invention are possible andis intended to include all those which are covered by the appendedclaims.

We claim:
 1. A communication network comprising:a first wirelessnetwork; a second wireless network independently operable from the firstwireless network; an access point device operable on the first wirelessnetwork; a first wireless device selectively communicating with theaccess point device on the first wireless network; a second wirelessdevice operable on the second wireless network to communicate with thefirst wireless device; and the first wireless device selectivelycommunicating with the second wireless device on the second wirelessnetwork after communicating an indication of unavailability on the firstwireless network to the access point device.
 2. The communicationnetwork of claim 1 wherein the indication of unavailability comprisessleep mode registration.
 3. The communication network of claim 2 whereinthe first wireless device also conducts sleep mode registration to entera power saving state.
 4. The communication network of claim 1 whereinthe access point device stores messages destined for the first wirelessdevice after receiving the indication of unavailability.
 5. Thecommunication network of claim 1 wherein, after participating on thesecond wireless network, the first wireless device communicates anindication of availability on the first wireless network to resumeparticipation on the first wireless network.
 6. The communicationnetwork of claim 5 wherein, after resuming participation on the firstwireless network, the access point device delivers stored messages tothe first wireless device via the first wireless network.
 7. Thecommunication network of claim 1 wherein the first wireless deviceparticipates as a master on the second wireless network.
 8. Thecommunication network of claim 1 wherein the first wireless deviceparticipates as a slave on the first wireless network.
 9. Acommunication network comprising:a first wireless link; a secondwireless link independent from the first wireless link; an access pointdevice; a first wireless device selectively communicating with theaccess point device on the first wireless link; a second wireless deviceoperable on the second wireless link; and the first wireless deviceselectively communicating an indication of unavailability on the firstwireless link prior to communicating on the second wireless link withthe second wireless device.
 10. The communication network of claim 9wherein the indication of unavailability comprises sleep moderegistration.
 11. The communication network of claim 10 wherein thefirst wireless device also conducts sleep mode registration to enter apower saving state.
 12. The communication network of claim 9 wherein theaccess point device stores messages destined for the first wirelessdevice after receiving the indication of unavailability.
 13. Thecommunication network of claim 9 wherein, after participating on thesecond wireless link, the first wireless device communicates anindication of availability on the first wireless link to resumeparticipation on the first wireless link.
 14. The communication networkof claim 13 wherein, after resuming participation on the first wirelesslink, the access point device delivers stored messages to the firstwireless device via the first wireless link.
 15. The communicationnetwork of claim 9 wherein the first wireless device participates as aslave on the first wireless link and a master on the second wirelesslink.
 16. In a communication network having an access point device, afirst wireless channel, a second wireless channel, and a network deviceoperable on the second wireless channel, a wireless devicecomprising:first transceiver circuitry that supports communication withthe access point on the first wireless channel and that communicates anindication of unavailability on the first wireless channel; and secondtransceiver circuitry coupled to the first transceiver circuitry thatcommunicates with the network device on the second wireless channelafter the first transceiver circuitry communicates the indication ofunavailability.
 17. The wireless device of claim 16 wherein theindication of unavailability comprises sleep mode registration.
 18. Thewireless device of claim 16 wherein the access point device storesmessages destined for the wireless device after receiving the indicationof unavailability.
 19. The wireless device of claim 16 wherein, afterparticipating on the second wireless channel, the wireless devicecommunicates an indication of availability on the first wireless channelto resume participation on the first wireless channel.
 20. The wirelessdevice of claim 19 wherein, after resuming participation on the firstwireless channel, the first transceiver circuitry is used to receivestored messages from the access point device via the first wirelesschannel.